Fix problems during unstable network

In this patch start and stop method is not raised exceptions
if connectivity problem is detected. Rasing exceptions there
exceptions are not expected by MessageHandlerServer.
It hangs server on start

Closes-Bug: #1553168

Change-Id: I891abab2a1184fa65b496ea2f7fc54894bc0b421

oslo_messaging/tests/drivers/pika/test_message.py

@@ -22,7 +22,7 @@ from oslo_serialization import jsonutils
 import pika
 
 import oslo_messaging
-from oslo_messaging._drivers.pika_driver import pika_engine
+from oslo_messaging._drivers.pika_driver import pika_commons as pika_drv_cmns
 from oslo_messaging._drivers.pika_driver import pika_message as pika_drv_msg
 
 
@@ -252,7 +252,7 @@ class RpcReplyPikaIncomingMessageTestCase(unittest.TestCase):
     def setUp(self):
         self._pika_engine = mock.Mock()
         self._pika_engine.allowed_remote_exmods = [
-            pika_engine._EXCEPTIONS_MODULE, "oslo_messaging.exceptions"
+            pika_drv_cmns.EXCEPTIONS_MODULE, "oslo_messaging.exceptions"
         ]
 
         self._channel = mock.Mock()

oslo_messaging/tests/drivers/pika/test_poller.py

@@ -12,6 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import socket
 import time
 import unittest
 
@@ -33,6 +34,18 @@ class PikaPollerTestCase(unittest.TestCase):
         )
         self._prefetch_count = 123
 
+    def test_start_when_connection_unavailable(self):
+        incoming_message_class_mock = mock.Mock()
+        poller = pika_poller.PikaPoller(
+            self._pika_engine, self._prefetch_count,
+            incoming_message_class=incoming_message_class_mock
+        )
+
+        self._pika_engine.create_connection.side_effect = socket.timeout()
+
+        # start() should not raise socket.timeout exception
+        poller.start()
+
     @mock.patch("oslo_messaging._drivers.pika_driver.pika_poller.PikaPoller."
                 "_declare_queue_binding")
     def test_poll(self, declare_queue_binding_mock):