Iabeb44f843c3c04f767c4103038fcf6c52966ff3 allowed snapshots to be
created from PAUSED non-volume backed instances but missed the volume
backed use case.
This change simply adds PAUSED to the list of acceptable vm_states when
creating a snapshot from a volume backed instance in addition to the
already supported ACTIVE, STOPPED and SUSPENDED vm_states.
Closes-Bug: #1878583
Change-Id: I9f95a054de9d43ecaa50ff7ffc9343490e212d53
(cherry picked from commit cfde53e4b4)