Implement Stack loading from DB as a separate function
Implement Stack loading from DB as a separate function

Separate out the lookup of a stack in the DB from the actual creation from
an existing DB representation.

Change-Id: I709fb7c4059229371ba85a2cd6e87ec5361a5400

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