Fix issue with ml2 plugin on using provider network

This commit fixes the issue that ml2 plugin
sets 'flat_networks' in ml2 configuration file as
empty.  The value of 'flat_networks' need to be set 
as the name of the physical network that was specified 
in the localrc file (or it's default value).

Change-Id: Ib4c31f6576da57534b36aefebd1ca8cd397c6c1a
diff --git a/lib/neutron_plugins/ml2 b/lib/neutron_plugins/ml2
index e3b2c4d..abe6ea7 100644
--- a/lib/neutron_plugins/ml2
+++ b/lib/neutron_plugins/ml2
@@ -89,7 +89,7 @@
 
     # Allow for setup the flat type network
     if [[ -z "$Q_ML2_PLUGIN_FLAT_TYPE_OPTIONS" && -n "$PHYSICAL_NETWORK" ]]; then
-            Q_ML2_PLUGIN_FLAT_TYPE_OPTIONS="flat_networks=$Q_ML2_FLAT_PHYSNET_OPTIONS"
+            Q_ML2_PLUGIN_FLAT_TYPE_OPTIONS="flat_networks=$PHYSICAL_NETWORK"
     fi
     # REVISIT(rkukura): Setting firewall_driver here for
     # neutron.agent.securitygroups_rpc.is_firewall_enabled() which is