Add test for ResourceDefinition equality

ResourceDefinition objects compare equal if they are generated from
equivalent templates. Only the MRO stands between us and disaster (since
both superclasses - ResourceDefinitionCore and collections.Mapping - define
__eq__ methods), so add a test to confirm that we are getting the correct
one.

Change-Id: I8181f91f08fd81104fe493539511d6fd129522c8
Merge "Add test for ResourceDefinition equality"