When a non-thinpool LVM container which have snapshotted clone is
destroyed, the LV of snapshotted clone was also deleted. This patch
prevent it.

The original non-thinpool LVM container of snapshotted clone cannot be
now destroyed.
Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>