Refactor instance tests to share common code
Refactor instance tests to share common code

Change-Id: I565f6aee43d07f3fc451538ca02f9398eedebaf3

pratikmallya/heat,NeCTAR-RC/heat,cryptickp/heat,rh-s/heat,ntt-sic/heat,maestro-hybrid-cloud/heat,openstack/heat,pshchelo/heat,JioCloud/heat,jasondunsmore/heat,noironetworks/heat,citrix-openstack-build/heat,ntt-sic/heat,steveb/heat,maestro-hybrid-cloud/heat,cwolferh/heat-scratch,dims/heat,srznew/heat,gonzolino/heat,miguelgrinberg/heat,redhat-openstack/heat,rickerc/heat_audit,rdo-management/heat,steveb/heat,citrix-openstack-build/heat,cryptickp/heat,varunarya10/heat,dragorosson/heat,dragorosson/heat,dims/heat,jasondunsmore/heat,openstack/heat,pshchelo/heat,takeshineshiro/heat,takeshineshiro/heat,cwolferh/heat-scratch,NeCTAR-RC/heat,rickerc/heat_audit,rh-s/heat,JioCloud/heat,varunarya10/heat,pratikmallya/heat,gonzolino/heat,srznew/heat,miguelgrinberg/heat,redhat-openstack/heat,noironetworks/heat,rdo-management/heat