Added RadosGW support

Originally https://github.com/crowbar/barclamp-ceph/pull/55

Partially ported from upstream cookbook.

Depends on https://github.com/crowbar/barclamp-keystone/pull/237
yes, it works with keystone patch, but please look onto https://github.com/crowbar/barclamp-ceph/pull/66/files#r15220420