Change to messagingv2 for oslo_messaging_notifications.driver

The oslo.messaging docs on the notification messaging driver
says that "messaging" (1.0) is a legacy format and you should
use messagingv2 unless otherwise required for that old format.

By default we should be testing with messagingv2.

Change-Id: I3031afe7551a0c8dde46e1ccfacff445fb68e122
diff --git a/lib/nova b/lib/nova
index 79f07f2..4c9f30f 100644
--- a/lib/nova
+++ b/lib/nova
@@ -575,7 +575,7 @@
 
     # Set the oslo messaging driver to the typical default. This does not
     # enable notifications, but it will allow them to function when enabled.
-    iniset $NOVA_CONF oslo_messaging_notifications driver "messaging"
+    iniset $NOVA_CONF oslo_messaging_notifications driver "messagingv2"
     iniset_rpc_backend nova $NOVA_CONF
     iniset $NOVA_CONF glance api_servers "${GLANCE_SERVICE_PROTOCOL}://${GLANCE_HOSTPORT}"