Simplify oslo.log configuration options

Use the preferred logging_user_identity_format option to specify an alternative context format
in log files.  The removal of defining logging_context_format_string brings this more inline
with optimal production configuration of using the defined default.  logging_user_identity_format
is set in devstack to maintain current compatibility of names instead of ids.

Change-Id: I3807d76b91b6cc1614b4a9a203509f8e1ad7146d
diff --git a/lib/neutron-legacy b/lib/neutron-legacy
index 692d5ea..978cbdb 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -963,7 +963,7 @@
         setup_colorized_logging $NEUTRON_CONF DEFAULT project_id
     else
         # Show user_name and project_name by default like in nova
-        iniset $NEUTRON_CONF DEFAULT logging_context_format_string "%(asctime)s.%(msecs)03d %(levelname)s %(name)s [%(request_id)s %(user_name)s %(project_name)s] %(instance)s%(message)s"
+        iniset $NEUTRON_CONF DEFAULT logging_user_identity_format "%(user_name)s %(project_name)s"
     fi
 
     if is_service_enabled tls-proxy; then