ovs_base: Fix debug-agent config for Q_USE_PROVIDERNET_FOR_PUBLIC=True

Set up external_network_bridge correctly for the case
of Q_USE_PROVIDERNET_FOR_PUBLIC=True.

This is an oversight in commit 6a633fd024347aade777ecd6545fa3efde5a959c.

Closes-Bug: #1394826
Change-Id: I33f0fe15bafb7071d8a09899d636471f49031606
diff --git a/lib/neutron_plugins/ovs_base b/lib/neutron_plugins/ovs_base
index f0ef194..07aa7cc 100644
--- a/lib/neutron_plugins/ovs_base
+++ b/lib/neutron_plugins/ovs_base
@@ -60,7 +60,11 @@
 }
 
 function _neutron_ovs_base_configure_debug_command {
-    iniset $NEUTRON_TEST_CONFIG_FILE DEFAULT external_network_bridge $PUBLIC_BRIDGE
+    if [ "$Q_USE_PROVIDERNET_FOR_PUBLIC" = "True" ]; then
+        iniset $NEUTRON_TEST_CONFIG_FILE DEFAULT external_network_bridge ""
+    else
+        iniset $NEUTRON_TEST_CONFIG_FILE DEFAULT external_network_bridge $PUBLIC_BRIDGE
+    fi
 }
 
 function _neutron_ovs_base_configure_firewall_driver {