Bugfix: use transport_url from [oslo_messaging_notifications] if present

According to https://docs.openstack.org/developer/oslo.messaging/opts.html#oslo-messaging-notifications
a transport_url defined in [oslo_messaging_notifications] should be used, if
present. In Ceilometer, this is ignored in favour of the transport_url defined
in [DEFAULT], which is a bug. This change fixes the bug.

Change-Id: I12a559ebbbc1edd18c6833943bb5e9af7adf4666

ceilometer/messaging.py

@@ -14,6 +14,7 @@
 # under the License.
 
 import oslo_messaging
+from oslo_messaging.notify import notifier
 from oslo_messaging import serializer as oslo_serializer
 
 DEFAULT_URL = "__default__"
@@ -31,7 +32,7 @@ def get_transport(conf, url=None, optional=False, cache=True):
     transport = TRANSPORTS.get(cache_key)
     if not transport or not cache:
         try:
-            transport = oslo_messaging.get_transport(conf, url)
+            transport = notifier.get_notification_transport(conf, url)
         except (oslo_messaging.InvalidTransportURL,
                 oslo_messaging.DriverLoadFailure):
             if not optional or url:

releasenotes/notes/use-notification-transport-url-489f3d31dc66c4d2.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - The transport_url defined in [oslo_messaging_notifications] was never used,
+    which contradicts the oslo_messaging documentation. This is now fixed.