Check for worker_service initialization

When stopping the engine check if the worker_service is
intialized or not before stopping it.

Change-Id: I876c2cef4bf6589b9bc45f58b5cd52ed0323c9e9
Closes-Bug: #1572851

heat/engine/service.py

@@ -420,7 +420,7 @@ class EngineService(service.Service):
     def stop(self):
         self._stop_rpc_server()
 
-        if cfg.CONF.convergence_engine:
+        if cfg.CONF.convergence_engine and self.worker_service:
             # Stop the WorkerService
             self.worker_service.stop()
 

heat/engine/worker.py

@@ -80,6 +80,8 @@ class WorkerService(service.Service):
         super(WorkerService, self).start()
 
     def stop(self):
+        if self._rpc_server is None:
+            return
         # Stop rpc connection at first for preventing new requests
         LOG.info(_LI("Stopping %(topic)s in engine %(engine)s."),
                  {'topic': self.topic, 'engine': self.engine_id})