BZ #1127862 - ceph client packages (compute, non-ha and ha controller)

https://bugzilla.redhat.com/show_bug.cgi?id=1127862

Unfortunately, glance::backend::rbd already includes one ceph client
package dependency, 'python-ceph'.  So, we tap dance around whether
glance::backend::rbd itself has been declared and thus declares
'python-ceph'.

Client packages include:

 librados2
 librbd1
 ceph-common
 python-ceph