Call db refresh in Stack object refresh
Call db refresh in Stack object refresh

The current Stack object refresh doesn't actually do any refreshing,
which explains the functional test speed regression since the RPC
nested stack code relies on stack.refresh() to poll for state change.

With this change AutoScalingSignalTest.test_signal_with_policy_update
locally takes ~60s consistently. Without this change ~50% of test runs
have some form of execution delay, taking 80s -> 300s+.

Change-Id: Ie06851fd5b0d8b802ebf701e8bf621562d9b6d88
Closes-Bug: #1433555

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