Address todo in compute cloud layer and move get_compute_usage to rely
to the proxy layer. With this change method returns Usage object instead
of munch. This also allows us to stop importing and inheriting from
normalize class here. "attached" filter of the search_floating_ips is
dopped since it is being pretty awkward.
Change-Id: I3de1654fc35b2985e4a0658f7117bbe9db554dd3