don't create a cinder type if already it exist

Avoid Puppet warnings by checking if a volume type exist before trying
to actually create it.

Closes-bug #1319857
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

Change-Id: Ib31db545d1d761fc6abed0a42dd7ae8e6cc0f25f