image: ensure notifier is really disable

On RHEL, notifier is at "qpid" but we need to disable it for now.
See https://github.com/enovance/puppet-openstack-cloud/issues/160

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge pull request #431 from enovance/disable-notifier-glance

image: ensure notifier is really disabled