Added RadosGW support

Originally https://github.com/crowbar/barclamp-ceph/pull/55

Partially ported from upstream cookbook.
So what I would do is:
- always include this recipe when keystone_instance is set
- look for the keystone node, and if `keystone_node[:keystone][:signing][:token_format] == "PKI"` is true, then includ soemthing like your ruby_block, except that I'd manually write the files in `nss_dir` to convert thanks to the `keystone_node[:keystone][:pki][:content][:signing_cert]` and `keystone_node[:keystone][:pki][:content][:ca]` attributes