After an unstack.sh several neutron services are left running. This
change tries to do a better (but not always successful) job of
stopping neutron agents.
stop_process does its own checking to see if a service is enabled
so we don't need to check before calling.
Change-Id: I8becbe9db56121cbc619a6d156b18f6c6d31a6e7
36891dc143