allow RadosGW and Ceph/RBD for Glance with vCenter

Only Ceph storage backends for Cinder and Nova should be disabled when
vCenter is used as the hypervisor, Ceph can still be used as storage
backend for Glance and for Swift/S3 object storage.

Change-Id: I5b77ad0a98673e331a5c3e5e7652c30ae2a96354
Closes-Bug: #1316377
Merge "allow RadosGW and Ceph/RBD for Glance with vCenter"