Set access_policy for messaging's dispatcher

Oslo messaging allow dispatcher to restrict endpoint methods
since 5.11.0 in https://review.openstack.org/#/c/358359/,
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: Ic9a3122a02dd1e5c76b45c04801f4c9b3ce8a757

karbor/rpc.py

@@ -25,6 +25,7 @@ __all__ = [
 
 from oslo_config import cfg
 import oslo_messaging as messaging
+from oslo_messaging.rpc import dispatcher
 from oslo_serialization import jsonutils
 
 import karbor.context
@@ -122,11 +123,13 @@ def get_client(target, version_cap=None, serializer=None):
 def get_server(target, endpoints, serializer=None):
     assert TRANSPORT is not None
     serializer = RequestContextSerializer(serializer)
+    access_policy = dispatcher.DefaultRPCAccessPolicy
     return messaging.get_rpc_server(TRANSPORT,
                                     target,
                                     endpoints,
                                     executor='eventlet',
-                                    serializer=serializer)
+                                    serializer=serializer,
+                                    access_policy=access_policy)
 
 
 def get_notifier(service=None, host=None, publisher_id=None):