Add notifications support

The change does not enable notifications, just configure right
transport url for it via oslo_messaging template.

Change-Id: I466404295a34fd7f4232e728469280b188ccf9af

service/files/keystone.conf.j2

@@ -27,8 +27,8 @@ provider = fernet
 driver = sql
 
 {% if keystone.notifications.enable %}
-{# This section should be updated after https://review.openstack.org/#/c/419995/ is merged #}
 [oslo_messaging_notifications]
 driver = messagingv2
-transport_url = rabbit://{{ rabbitmq.user }}:{{ rabbitmq.password }}@{{ address('rabbitmq', rabbitmq.port) }}
 {% endif %}
+
+{{ oslo_messaging[messaging.backend.notifications]('notifications_config') }}

service/keystone.yaml

@@ -53,6 +53,9 @@ service:
       daemon:
         dependencies:
           - memcached
+          # {% if keystone.notifications.enable -%}
+          - "{{ messaging.dependencies[messaging.backend.notifications] }}"
+          # {%- endif %}
         files:
           - keystone-conf
           - wsgi-keystone-conf