Redundant check in os-migrate_volume_completion

Remove the redundant check for 'migrate_volume_completion', and add the UT
for it.

Change-Id: I6b643dbf9ae1302cafe6748a361123d7d76c437f
Closes-Bug: #1254963
Merge "Redundant check in os-migrate_volume_completion"
(Test commit) Change README to reflect Jio's fork of Cinder

Change-Id: I3f26c0a736e63725aec24ca2fa12c707b8e6460f