Perform additional check before live snapshotting

Bug 1193146

Move blockJobAbort() out of the _live_snapshot function, such that
it continues to terminate existing jobs, while also doubling as a
method for confirming that our version of Qemu/KVM is new enough to
execute a _live_snapshot.

Change-Id: Ife5d2fd768a34dabf25a1bfc24e54bd6db762c89
Merge "Perform additional check before live snapshotting"