fix for issue 786

Added a role look up when setting the notifications topics. If the role lookup returns a value other than 0 when searching for "single-controller" the notification topic will be set to "glance_notifications" otherwise the topic is set to whatever the user set for "glance["api"]["notification_topic"]", default is "notifications" 

This PR is to fix : https://github.com/rcbops/chef-cookbooks/issues/786