Use common rpc pattern for all services

There is a commonly shared and proven rpc pattern used
across most OpenStack services that is already implemented
in watcher, but the functions are not used.

This patch basically makes use of the existing
rpc classes and removes some unnecessary code.

Change-Id: I57424561e0675a836d10b712ef1579a334f72018

watcher/tests/common/test_service.py

@@ -20,7 +20,6 @@ from unittest import mock
 from oslo_config import cfg
 
 import oslo_messaging as om
-from watcher.common import rpc
 from watcher.common import service
 from watcher import objects
 from watcher.tests import base
@@ -102,8 +101,6 @@ class TestService(base.TestCase):
 
     def test_init_service(self):
         dummy_service = service.Service(DummyManager)
-        self.assertIsInstance(dummy_service.serializer,
-                              rpc.RequestContextSerializer)
         self.assertIsInstance(
             dummy_service.conductor_topic_handler,
             om.rpc.server.RPCServer)