Provide unified _show_resource()

Now every neutron resources has to override the method _show_resource() due neutronclient has a different way to get the info of resource:
     neutronclient: 'self.client().show_port()', 'self.client().show_network()' and so on
     otherclients: 'self.client().*entity*.get()'
This blueprint will refactor and provide unified a method for all neutron resources, it is not hard, because it's regular.