Increase num_engine_workers to 4 in functional tests
Increase num_engine_workers to 4 in functional tests

In convergence testing 2 seems to be causing RPC Message timeouts.

Change-Id: Ic989bc42662ec19db5c78d77a7d648227f4ab5e3

steveb/heat,cryptickp/heat,maestro-hybrid-cloud/heat,dims/heat,takeshineshiro/heat,pratikmallya/heat,jasondunsmore/heat,noironetworks/heat,pratikmallya/heat,dragorosson/heat,cryptickp/heat,maestro-hybrid-cloud/heat,gonzolino/heat,openstack/heat,dragorosson/heat,miguelgrinberg/heat,takeshineshiro/heat,cwolferh/heat-scratch,miguelgrinberg/heat,steveb/heat,noironetworks/heat,cwolferh/heat-scratch,openstack/heat,gonzolino/heat,dims/heat,jasondunsmore/heat