Keystone: it enables keystone notificaitons

This patch sets the notifier driver to messagingv2 so all
messages sent to RabbitMQ using the 2.0 format.

For info:
Auth notificaitons are supressed by default, to enable it
uncomment the following parameter:
conf:
  DEFAULT:
    notification_opt_out: ""

Change-Id: I652fc34a229612dcb8b96c8722b8c6ac1c8aba3e
Signed-off-by: Ruslan Khanbikov <rk760n@att.com>

keystone/values.yaml

@@ -342,6 +342,8 @@ conf:
     DEFAULT:
       log_config_append: /etc/keystone/logging.conf
       max_token_size: 255
+      #NOTE(rk760n): if you need auth notifications to be sent, uncomment it
+      #notification_opt_out: ""
     token:
       provider: fernet
       # 12 hours
@@ -358,6 +360,8 @@ conf:
     cache:
       enabled: true
       backend: dogpile.cache.memcached
+    oslo_messaging_notifications:
+      driver: messagingv2
   # NOTE(lamt) We can leverage multiple domains with different
   # configurations as outlined in
   # https://docs.openstack.org/keystone/pike/admin/identity-domain-specific-config.html.