attachment_create fails on live migration with bfv instance

[Steve Noyes]

While testing live migration with the new v3 cinder api, I found that migrating an instance that was booted from a volume (bfv) fails during pre_live_migration. The problem happens when we are creating a new attachment (attachment_create) to attach the volume on the destination host. The attachment_create fails because the volume's status is 'in-use' and attachment create wants it to be available or downloading.

(This is similar to the reserve issue - https://review.openstack.org/#/c/469252/, bug 1694530)

^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m File "/mnt/share/stack/nova/nova/volume/cinder.py", line 579, in attachment_create
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m volume_id, connector, instance_id)
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m File "/mnt/share/stack/python-cinderclient/cinderclient/v3/attachments.py", line 33, in create
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m retval = self._create('/attachments', body, 'attachment')
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m File "/mnt/share/stack/python-cinderclient/cinderclient/base.py", line 323, in _create
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m resp, body = self.api.client.post(url, body=body)
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m File "/mnt/share/stack/python-cinderclient/cinderclient/client.py", line 178, in post
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m return self._cs_request(url, 'POST', **kwargs)
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m File "/mnt/share/stack/python-cinderclient/cinderclient/client.py", line 166, in _cs_request
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m return self.request(url, method, **kwargs)
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m File "/mnt/share/stack/python-cinderclient/cinderclient/client.py", line 155, in request
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m raise exceptions.from_response(resp, body)
^[[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00mClientException: Unable to create attachment for volume (Invalid volume: Volume 383f401e-7efd-49a7-8f8f-bbde13bc6d75 status must be available or downloading). (HTTP 500) (Request-ID: req-d3d8da11-0f9e-4d53-999b-925aac21b9cb)
^[vailable or downloading[01;31m2017-06-12 14:09:57.141 TRACE oslo_messaging.rpc.server ^[[01;35m^[[00m