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/neutron-legacy b/lib/neutron-legacy
index b381b64..1a16a44 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -798,7 +798,7 @@
 }
 
 function _configure_neutron_ceilometer_notifications {
-    iniset $NEUTRON_CONF oslo_messaging_notifications driver messaging
+    iniset $NEUTRON_CONF oslo_messaging_notifications driver messagingv2
 }
 
 function _configure_neutron_metering {