Added notification_level config option

In this changeset, I implemented the notification_level parameter
that allows you to set the level minimum level of notification to
be emitted by Watcher.

Partially Implements: blueprint watcher-notifications-ovo

Change-Id: I78b30ceb3ee7606078a87beb3a4ce5d9568af1e0

watcher/common/rpc.py

@@ -72,8 +72,12 @@ def init(conf):
         aliases=TRANSPORT_ALIASES)
 
     serializer = RequestContextSerializer(JsonPayloadSerializer())
-    NOTIFIER = messaging.Notifier(NOTIFICATION_TRANSPORT,
-                                  serializer=serializer)
+    if not conf.notification_level:
+        NOTIFIER = messaging.Notifier(
+            NOTIFICATION_TRANSPORT, serializer=serializer, driver='noop')
+    else:
+        NOTIFIER = messaging.Notifier(NOTIFICATION_TRANSPORT,
+                                      serializer=serializer)
 
 
 def initialized():