effectively disable libvirt live snapshotting

As being seen in the gate, libvirt 1.2.2 doesn't appear to actually
handle live snapshotting under any appreciable load (possibly
related to parallel operations). It isn't a 100% failure, but it's
currently being hit in a large number of runs.

Effectively turn this off by increasing the
MIN_LIBVIRT_LIVESNAPSHOT_VERSION to something that doesn't yet
exist. This can get us back to a working state, then we can decide
if live snapshotting is something that can be made to actually work
under load.

DocImpact

Related-Bug: #1334398

Change-Id: I9908b743df2093c8dd2723af89be51630eafc99f
Merge "effectively disable libvirt live snapshotting"