Fix the notifier example
Fix the notifier example

The notifier should be instantiated using messaging.Notifier, not
notifier.Notifier.

Change-Id: Id1930df6b758b292a7591e2e4cba2ef5a313a3cb

dukhlov/oslo.messaging,magic0704/oslo.messaging,dims/oslo.messaging,stevei101/oslo.messaging,zhurongze/oslo.messaging,redhat-openstack/oslo.messaging,ozamiatin/oslo.messaging,redhat-openstack/oslo.messaging,magic0704/oslo.messaging,isyippee/oslo.messaging,dims/oslo.messaging,hkumarmk/oslo.messaging,hkumarmk/oslo.messaging,viggates/oslo.messaging,eayunstack/oslo.messaging,stevei101/oslo.messaging,isyippee/oslo.messaging,apporc/oslo.messaging,dukhlov/oslo.messaging,apporc/oslo.messaging,ozamiatin/oslo.messaging,zhurongze/oslo.messaging