Fixes agent_notification_service_name

This patch corrects the service name of the ceilometer notification
agent, which was 'ceilometer-agent-notification' in pre-release RPMs but
was later changed to 'ceilometer-notification'.

Change-Id: Ie2703a028ce154efa7fa1d0da58914230adfc7db
(cherry picked from commit 00bfaa1fa4709cec6a03e2772445dc8f27a89224)