Added RadosGW support

Originally https://github.com/crowbar/barclamp-ceph/pull/55

Partially ported from upstream cookbook.
> But this is still wrong: what we care about is keystone being deployed in this SUSE Cloud 

Really? Before, you wanted to raise an error if keystone is not avialable on this node...

> But you're not using the node[:keystone][:signing] attributes here.

I know. That was me pointing out that I forgot to convert all the block in the same way. Anyway, the question is, should I use fixed paths here?