core: Deprecate broken snapshots upgrade script

In order to deprecate broken status of snapshots:
* Added an upgrade script for setting disks of broken
  snapshots as illegal.
* SnapshotVmConfigurationHelper:
  Update image status from DB on returned disks
  (for proper indication for disks status).
* TryBackToAllSnapshotsOfVmCommand:
  Added validation for images that are upon to be previewed.

Change-Id: Ia91153b1c3c363bca2d947974e6a67c459dba008
Bug-Url: https://bugzilla.redhat.com/1056935
Signed-off-by: Daniel Erez <derez@redhat.com>