Fixed a problem in terminate_connection in VMAX driver

The VMAX driver unmaps the volume from the wrong VM in
terminate_connection during live migration. This patche
fixed this problem.

Closes-Bug: #1395845
Change-Id: Ida7136165b959a9e0d7d50c240b447bf237caa6c
Merge "Fixed a problem in terminate_connection in VMAX driver"