Continue reserving H6xx namespace for calling methods

H6xx is reserved for calling methods (see
http://docs.openstack.org/developer/hacking/#calling-methods), so move
the three H6xx tests to more approrate locations.

H601=>H903
H602=>H234 since the issue is that python3 gives an explicit warning
H603=>H235 same reason as H234

Since only H601 has been released, this will have a minor impact

Change-Id: Ie68c9b4421f615b6d76cfb400408c951fc335eeb