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
one example is [here](https://github.com/MaximilianMeister/barclamp-neutron/blob/feature/deactivate-services/chef/data_bags/crowbar/migrate/neutron/011_change_role_removal_priority.rb#L2) and part of a migration as well. I will do that for ceph too probably, but havent touched it yet.
so I think there is no problem here with setting the `['element_run_list_order']`