core: unlock_entity should unlock unattached disks

unlock_entity.sh script does not unlock locked images that are not
attached to any VM.

The script should unlock any disks, even such that were created and are
not attached to a VM.

Change-Id: I8346f0ae34a7b2ea9d4ce4281dbebdb67a554ac0
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1032910
Signed-off-by: Eli Mesika <emesika@redhat.com>