Added RadosGW support

Originally https://github.com/crowbar/barclamp-ceph/pull/55

Partially ported from upstream cookbook.
Two issues here:
- this is about the signing certificate, not the SSL certificate for the keystone server. These are two different things. So using the attribute like you are is wrong.
- on top of that, using the attribute is wrong because, again, keystone might not be deployed on this node so the attribute would just not exist.

Instead, we should fix the keystone recipe to have the files as attributes (we already do that in the HA case, see `ruby_block "synchronize PKI keys for founder" do` in keystone cookbook). And btw, we should only do this when using PKI for keystone.