live-migration fails when FC multipath is used

[Jeegn Chen]

I tried live-migration against VM with multipath access to FC bootable volume and FC data volume.
After checking the code, I found the reason is that
1. /dev/dm-<NUM> is used, which is subject to change in the destination Compute Node since it is not unique across nodes
2. multipath_id in connnection_info is not maintained properly and may be lost during connection refreshing

The fix would be
1. Like iSCSI multipath, use /dev/mapper/<multipath_id> instead of /dev/dm-<NUM>
2. Since multipath_id is unique for a volume no matter where it is attached, add logic to preserve this information.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/98738

[OpenStack Infra (hudson-openstack)]

Change abandoned by Jeegn Chen (<email address hidden>) on branch: master
Review: https://review.openstack.org/98738
Reason: Some changes are missing. Need revise

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/98738
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=3ea14e8a70a946dbb162ecafa848e4f2fa29772a
Submitter: Jenkins
Branch: master

commit 3ea14e8a70a946dbb162ecafa848e4f2fa29772a
Author: Jeegn Chen <email address hidden>
Date: Sun Jun 8 16:23:36 2014 +0800

    Fix live-migration failure in FC multipath case

    Currently, /dev/dm-<NUM> instead of /dev/mapper/<multipath_id> is
    used to access multipath FC volumes by Compute Node and
    multipath_id in connection_info is not maintained properly and
    may be lost during connection refreshing.

    This implementation will make source Compute Node and destination
    Compute Node fail to disconnect/connect to volumes properly and
    result in live-migration failure.

    To fix it, /dev/mapper<multipath_id> will be used instead of
    /dev/dm-<NUM> to access multipath devices, just like iSCSI multipath
    implementation, and logic to preserve the unique (across Compute
    Nodes) multipath_id is also added.

    Change-Id: I17f15852c098af88afd270084c62eb87693c60d4
    Closes-Bug: #1327497

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/icehouse
Review: https://review.openstack.org/123056

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/123056
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=74e0ba7e658fcd2c6d1b7a92dcee564098d0a1ff
Submitter: Jenkins
Branch: stable/icehouse

commit 74e0ba7e658fcd2c6d1b7a92dcee564098d0a1ff
Author: Jeegn Chen <email address hidden>
Date: Sun Jun 8 16:23:36 2014 +0800

    Fix live-migration failure in FC multipath case

    Currently, /dev/dm-<NUM> instead of /dev/mapper/<multipath_id> is
    used to access multipath FC volumes by Compute Node and
    multipath_id in connection_info is not maintained properly and
    may be lost during connection refreshing.

    This implementation will make source Compute Node and destination
    Compute Node fail to disconnect/connect to volumes properly and
    result in live-migration failure.

    To fix it, /dev/mapper<multipath_id> will be used instead of
    /dev/dm-<NUM> to access multipath devices, just like iSCSI multipath
    implementation, and logic to preserve the unique (across Compute
    Nodes) multipath_id is also added.

    Closes-Bug: #1327497
    (cherry picked from commit 3ea14e8a70a946dbb162ecafa848e4f2fa29772a)

    Conflicts:
     nova/storage/linuxscsi.py
     nova/tests/virt/libvirt/test_libvirt_volume.py
     nova/virt/block_device.py
     nova/virt/libvirt/volume.py

    This backport commit adjust oslo.i18n usage to oslo-incubator common code,
    due to we didn't have oslo.i18n in icehouse.
    And remove unused variable value dev_str in test_libvirt_volume.py,
    it should be deleted but not worth a specific commit in stable/icehouse.

    Change-Id: I17f15852c098af88afd270084c62eb87693c60d4