Neutron: include metering service plugin in conf

The common code for metering calls _neutron_service_plugin_class_add,
which despite the description only just appends a service plugin to
$Q_SERVICE_PLUGIN_CLASSES - it doesn't actually write it into a
configuration file.

So for now, read out the configuration, and append metering to it, then
write it back out.

Change-Id: Ice96cca8b43dcd54f2aa81461000a4597db8260d
diff --git a/lib/neutron b/lib/neutron
index ad68d8e..5cab8e1 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -245,6 +245,12 @@
         source $TOP_DIR/lib/neutron_plugins/services/metering
         neutron_agent_metering_configure_common
         neutron_agent_metering_configure_agent
+        # TODO(sc68cal) hack because we don't pass around
+        # $Q_SERVICE_PLUGIN_CLASSES like -legacy does
+        local plugins=""
+        plugins=$(iniget $NEUTRON_CONF DEFAULT service_plugins)
+        plugins+=",metering"
+        iniset $NEUTRON_CONF DEFAULT service_plugins $plugins
     fi
 
 }