Set access_policy for messaging's dispatcher

oslo.messaging allow dispatcher to restrict endpoint methods since
5.11.0 in d3a8f280ebd6fd12865fd20c4d772774e39aefa2, set with
DefaultRPCAccessPolicy to fix FutureWarning like:

"The access_policy argument is changing its default value to <class
'oslo_messaging.rpc.dispatcher.DefaultRPCAccessPolicy'> in version '?',
please update the code to explicitly set None as the value:
access_policy defaults to LegacyRPCAccessPolicy which exposes private
methods. Explicitly set access_policy to DefaultRPCAccessPolicy or
ExplicitRPCAccessPolicy.

Change-Id: I169d187c757dc97f447dad9a441a3d8d7e91b046

heat/common/messaging.py

@@ -16,6 +16,7 @@
 import eventlet
 from oslo_config import cfg
 import oslo_messaging
+from oslo_messaging.rpc import dispatcher
 from oslo_serialization import jsonutils
 from osprofiler import profiler
 
@@ -129,9 +130,11 @@ def cleanup():
 def get_rpc_server(target, endpoint):
     """Return a configured oslo_messaging rpc server."""
     serializer = RequestContextSerializer(JsonPayloadSerializer())
+    access_policy = dispatcher.DefaultRPCAccessPolicy
     return oslo_messaging.get_rpc_server(TRANSPORT, target, [endpoint],
                                          executor='eventlet',
-                                         serializer=serializer)
+                                         serializer=serializer,
+                                         access_policy=access_policy)
 
 
 def get_rpc_client(**kwargs):