reproduce this bug steps:
1、I have two hosts and both hosts are installed cinder-volume.
[root@2C5_10_DELL05 cinder(keystone_admin)]# cinder service-list
+------------------+-----------------------------------+------+----------+-------+----------------------------+-----------------+
|      Binary      |                Host               | Zone |  Status  | State |         Updated_at         | Disabled Reason |
+------------------+-----------------------------------+------+----------+-------+----------------------------+-----------------+
| cinder-scheduler |           2C5_10_DELL05           | nova | enabled  |   up  | 2016-05-09T11:48:31.000000 |       None      |
|  cinder-volume   | 2C5-10_DELL01@KS3200ISCSIDriver-2 | nova | enabled  |   up  | 2016-05-09T11:49:16.000000 |       None      |
|  cinder-volume   |         2C5-10_DELL01@lvm         | nova | disabled |   up  | 2016-05-09T11:49:17.000000 |       None      |
|  cinder-volume   |           2C5_10_DELL05           | nova | enabled  |  down | 2016-05-06T03:02:08.000000 |       None      |
|  cinder-volume   |  2C5_10_DELL05@FJDXISCSIDriver-1  | nova | enabled  |   up  | 2016-05-09T11:48:29.000000 |       None      |
|  cinder-volume   |  2C5_10_DELL05@FJDXISCSIDriver-2  | nova | enabled  |   up  | 2016-05-09T11:48:29.000000 |       None      |
|  cinder-volume   | 2C5_10_DELL05@KS3200ISCSIDriver-1 | nova | enabled  |   up  | 2016-05-09T11:48:29.000000 |       None      |
|  cinder-volume   | 2C5_10_DELL05@KS3200ISCSIDriver-2 | nova | enabled  |   up  | 2016-05-09T11:48:30.000000 |       None      |
|  cinder-volume   |         2C5_10_DELL05@lvm         | nova | enabled  |   up  | 2016-05-09T11:48:32.000000 |       None      |
+------------------+-----------------------------------+------+----------+-------+----------------------------+-----------------+
2.The host "2C5_10_DELL05" driver use support "pools" version. I create a volume in the host.
[root@2C5_10_DELL05 cinder(keystone_admin)]# cinder show eb7e638b-8385-4c73-8b60-1c4c9e89a072
+---------------------------------------+------------------------------------------------------------------------+
|                Property               |                                 Value                                  |
+---------------------------------------+------------------------------------------------------------------------+
|              attachments              |                                   []                                   |
|           availability_zone           |                                  nova                                  |
|                bootable               |                                 false                                  |
|          consistencygroup_id          |                                  None                                  |
|               created_at              |                       2016-05-09T01:10:59.000000                       |
|              description              |                                  None                                  |
|               encrypted               |                                 False                                  |
|                   id                  |                  eb7e638b-8385-4c73-8b60-1c4c9e89a072                  |
|                metadata               | {u'volname': u'OpenCos_R6775347838262577007', u'vdname': u'ipsan_vd2'} |
|              multiattach              |                                 False                                  |
|                  name                 |                               test_zy22                                |
|         os-vol-host-attr:host         |              2C5_10_DELL05@KS3200ISCSIDriver-2#ipsan_vd2               |
|     os-vol-mig-status-attr:migstat    |                                 error                                  |
|     os-vol-mig-status-attr:name_id    |                  6581e25b-2744-4648-8b49-23fc834da6fc                  |
|      os-vol-tenant-attr:tenant_id     |                    853481fe4d1e4d1eb0136c7ecf46e5e7                    |
|   os-volume-replication:driver_data   |                                  None                                  |
| os-volume-replication:extended_status |                                  None                                  |
|           replication_status          |                                disabled                                |
|                  size                 |                                   1                                    |
|              snapshot_id              |                                  None                                  |
|              source_volid             |                                  None                                  |
|                 status                |                               available                                |
|                user_id                |                    95d365ac3e3948c9be554a33855c6e07                    |
|              volume_type              |                                  ksip                                  |
+---------------------------------------+------------------------------------------------------------------------+

3. The other host(2C5-10_DELL01)use the older driver version(haven't supported the pools)
4. I migrate the volume to the step3 host.
cinder migrate eb7e638b-8385-4c73-8b60-1c4c9e89a072  2C5-10_DELL01@KS3200ISCSIDriver-2#KS3200_IPSAN
5. migrate failed.
   [root@2C5_10_DELL05 cinder(keystone_admin)]# cinder show eb7e638b-8385-4c73-8b60-1c4c9e89a072
+---------------------------------------+------------------------------------------------------------------------+
|                Property               |                                 Value                                  |
+---------------------------------------+------------------------------------------------------------------------+
|              attachments              |                                   []                                   |
|           availability_zone           |                                  nova                                  |
|                bootable               |                                 false                                  |
|          consistencygroup_id          |                                  None                                  |
|               created_at              |                       2016-05-09T01:10:59.000000                       |
|              description              |                                  None                                  |
|               encrypted               |                                 False                                  |
|                   id                  |                  eb7e638b-8385-4c73-8b60-1c4c9e89a072                  |
|                metadata               | {u'volname': u'OpenCos_R6775347838262577007', u'vdname': u'ipsan_vd2'} |
|              multiattach              |                                 False                                  |
|                  name                 |                               test_zy22                                |
|         os-vol-host-attr:host         |              2C5_10_DELL05@KS3200ISCSIDriver-2#ipsan_vd2               |
|     os-vol-mig-status-attr:migstat    |                                 error                                  |
|     os-vol-mig-status-attr:name_id    |                  6581e25b-2744-4648-8b49-23fc834da6fc                  |
|      os-vol-tenant-attr:tenant_id     |                    853481fe4d1e4d1eb0136c7ecf46e5e7                    |
|   os-volume-replication:driver_data   |                                  None                                  |
| os-volume-replication:extended_status |                                  None                                  |
|           replication_status          |                                disabled                                |
|                  size                 |                                   1                                    |
|              snapshot_id              |                                  None                                  |
|              source_volid             |                                  None                                  |
|                 status                |                               available                                |
|                user_id                |                    95d365ac3e3948c9be554a33855c6e07                    |
|              volume_type              |                                  ksip                                  |
+---------------------------------------+------------------------------------------------------------------------+
The scheduler log as following:
2016-05-09 19:40:24.610 14702 ERROR cinder.scheduler.manager [req-1bc39a54-1c4b-44a6-88e9-e480067ce12a 95d365ac3e3948c9be554a33855c6e07 853481fe4d1e4d1eb0136c7ecf46e5e7 - - -] Failed to schedule_migrate_volume_to_host: No valid host was found. Cannot place volume eb7e638b-8385-4c73-8b60-1c4c9e89a072 on 2C5-10_DELL01@KS3200ISCSIDriver-2#KS3200_IPSAN