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
```
    keystone_node[:keystone][:pki] ||= {}
    keystone_node[:keystone][:pki][:content] ||= {}
```