core: Live Merge recovery flow

When a VM stops running during a live merge, check the status using a
new reconcileVolumeChain vdsm verb.  This verb will ensure the volume
chain is correct and return the comprising images, which we can then use
to converge the Live Merge flow while the VM is still down.

Change-Id: Ie858c69412698e9a11a7f52ee88c3c078b3f2303
Bug-Url: https://bugzilla.redhat.com/1129898
Signed-off-by: Greg Padgett <gpadgett@redhat.com>