Do not create cinder-volumes if not needed

When CONFIG_CINDER_VOLUMES_CREATE=n, Packstack tries to create
cinder-volumes anyway after commit
58bd73af9757e7031aa29d252bc318953c39639d .

Change-Id: I4d385b45024602539c85164d9fe410fda510bab1
Merge "Do not create cinder-volumes if not needed"