make notifier default event publisher

direct publisher is mainly for testing and was used for event
pipeline to maintain consistency with previous functionality. this
patch makes notifier default to move storage load to collector
where it should be.

Change-Id: I2b12ac8afcd6e66e36d03276198f2d8e310b518f

etc/ceilometer/event_pipeline.yaml

@@ -10,4 +10,4 @@ sinks:
       transformers:
       triggers:
       publishers:
-          - direct://
+          - notifier://