Don't set external_network_bridge by default

Since the empty value is the default for the option, and when explcitly
set in config file, it triggers a deprecation warning for the option,
avoid setting it unless we actually need to override the new default
value.

Change-Id: If423114d7a52da29b97d1fb473a955d9d69a1a3e
diff --git a/lib/neutron_plugins/brocade b/lib/neutron_plugins/brocade
index 1b42e77..310b72e 100644
--- a/lib/neutron_plugins/brocade
+++ b/lib/neutron_plugins/brocade
@@ -54,7 +54,6 @@
 }
 
 function neutron_plugin_configure_l3_agent {
-    iniset $Q_L3_CONF_FILE DEFAULT external_network_bridge
     iniset $Q_L3_CONF_FILE DEFAULT l3_agent_manager neutron.agent.l3_agent.L3NATAgentWithStateReport
 }
 
diff --git a/lib/neutron_plugins/linuxbridge_agent b/lib/neutron_plugins/linuxbridge_agent
index f121637..dfed49b 100755
--- a/lib/neutron_plugins/linuxbridge_agent
+++ b/lib/neutron_plugins/linuxbridge_agent
@@ -48,7 +48,6 @@
     local conf_file=$1
     sudo brctl addbr $PUBLIC_BRIDGE
     set_mtu $PUBLIC_BRIDGE $PUBLIC_BRIDGE_MTU
-    iniset $conf_file DEFAULT external_network_bridge
 }
 
 function neutron_plugin_configure_plugin_agent {
diff --git a/lib/neutron_plugins/ovs_base b/lib/neutron_plugins/ovs_base
index 795d2bb..1a97001 100644
--- a/lib/neutron_plugins/ovs_base
+++ b/lib/neutron_plugins/ovs_base
@@ -87,9 +87,7 @@
 }
 
 function _neutron_ovs_base_configure_l3_agent {
-    if [ "$Q_USE_PROVIDERNET_FOR_PUBLIC" = "True" ]; then
-        iniset $Q_L3_CONF_FILE DEFAULT external_network_bridge ""
-    else
+    if [ "$Q_USE_PROVIDERNET_FOR_PUBLIC" != "True" ]; then
         iniset $Q_L3_CONF_FILE DEFAULT external_network_bridge $PUBLIC_BRIDGE
     fi