Fix mocking requests in test_engine_service
Fix mocking requests in test_engine_service

After commit Icf51dfd35423ac33a9126731862a90525c17306c
requests not in service's imports, so mocking
service.requests is wrong. This patch fix the situation.
Also change mocking db_api from service_software_config.

Change-Id: Ic9ac0a9ee48671716c4c1ae3517b3e5377a96b38

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