refactor test_engine_service.py

refactor tests based on stackServiceTestBase to be more like
the other tests, ie clear mocking, validation, and just
inherit from HeatTestCase rather than inheriting lots of
stuff from a base class, which isn't needed for all the tests

Fixes bug #1180375

Change-Id: I78ade1c53113f8f72b4df8ff346c45ec93f19393