engine : Live Merge fails to find cotr for RemoveSnapshotSingleDiskLiveCommand

Live deletion of a snapshot (live merge) fails to
find constructor for RemoveSnapshotSingleDiskLiveCommand

Change-Id: I8b1053621030049ed2e04de3fb5965f98a33ad05
Bug-Url: https://bugzilla.redhat.com/1115127
Signed-off-by: Ravi Nori <rnori@redhat.com>