Cherry-pick glance/pull/193 - fix for issue rcbops/chef-cookbooks/#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 mentions rcbops/chef-cookbooks#786