Make test notifier useful

We need a way to query what notifications were sent to the test notifier
and later clear out that list.

oslo/messaging/notify/_impl_test.py

@@ -17,14 +17,18 @@
 
 from oslo.messaging.notify import notifier
 
+NOTIFICATIONS = []
+
+
+def reset():
+    "Clear out the list of recorded notifications."
+    global NOTIFICATIONS
+    NOTIFICATIONS = []
+
 
 class TestDriver(notifier._Driver):
 
     "Store notifications in memory for test verification."
 
-    def __init__(self, conf, **kwargs):
-        super(TestDriver, self).__init__(conf, **kwargs)
-        self.notifications = []
-
     def notify(self, ctxt, message, priority):
-        self.notifications.append(message)
+        NOTIFICATIONS.append((ctxt, message, priority))