Expose _impl_test for designate

The previous attempt to do this in
Ide40b293c9b9c76aae094950720cead4179ea883 created a new module
oslo/messaging/notify/_impl_test.py which imported the symbols from
oslo_messaging/notify/_impl_test.py. That doesn't actually work, because
the functions to reset the notifications modify the copy of the symbol
in the oslo_messaging package, but the designate tests are still looking
at the copy in oslo/messaging.

This change imports a copy of the module from oslo_messaging in the
oslo/messaging namespace to make certain that the same module object,
and therefore the same global data structure, is used no matter which
path the code is accessed.

The designate team still needs to fix their fixture, but this will let
us release oslo.messaging without breaking their tests in the mean time.

Partial-Bug: #1412812

Change-Id: I629ac57ae1e74bb07e5e98ee2fbc21f8421c3c24

oslo/messaging/notify/__init__.py

@@ -25,3 +25,4 @@ from .listener import *
 from .log_handler import *
 from .logger import *
 from .dispatcher import NotificationResult
+from oslo_messaging.notify import _impl_test

oslo/messaging/notify/_impl_test.py

@@ -1,13 +0,0 @@
-#    Licensed under the Apache License, Version 2.0 (the "License"); you may
-#    not use this file except in compliance with the License. You may obtain
-#    a copy of the License at
-#
-#         http://www.apache.org/licenses/LICENSE-2.0
-#
-#    Unless required by applicable law or agreed to in writing, software
-#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-#    License for the specific language governing permissions and limitations
-#    under the License.
-
-from oslo_messaging.notify._impl_test import *  # noqa