Rework stack_resource *complete method unit tests
Rework stack_resource *complete method unit tests

This makes the tests more consistent and more like a unit test.

Part of blueprint decouple-nested
Change-Id: If77b6fa32515c376ee17b5502db8e0f373525845

cwolferh/heat-scratch,steveb/heat,srznew/heat,openstack/heat,pratikmallya/heat,noironetworks/heat,dragorosson/heat,maestro-hybrid-cloud/heat,steveb/heat,miguelgrinberg/heat,srznew/heat,rh-s/heat,rdo-management/heat,miguelgrinberg/heat,pshchelo/heat,maestro-hybrid-cloud/heat,gonzolino/heat,rh-s/heat,pratikmallya/heat,openstack/heat,cryptickp/heat,dims/heat,cryptickp/heat,takeshineshiro/heat,jasondunsmore/heat,takeshineshiro/heat,dims/heat,dragorosson/heat,noironetworks/heat,rdo-management/heat,gonzolino/heat,pshchelo/heat,cwolferh/heat-scratch,jasondunsmore/heat