migration: Recover block devices if failure in device state

migration: Recover block devices if failure in device state

In e91d895 I added the new pause-before-switchover mechanism
to allow migration completion to be delayed; this changes the
last state prior to completion to MIGRATE_STATUS_DEVICE rather
than MIGRATE_STATUS_ACTIVE.

Fix the failure path in migration_completion to recover the block
devices if it fails in MIGRATE_STATUS_DEVICE, not just the
MIGRATE_STATUS_ACTIVE that it previously had.

This corresponds to rh bz:
  https://bugzilla.redhat.com/show_bug.cgi?id=1538494
whose symptom is an occasional source crash on a failed migration.

Fixes: e91d8951d59d483f085f
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
(cherry picked from commit 6039dd5b1c45d76403b9dcadd2afd7efd8f42330)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>