Fix stevedore warning with neutron firewall_driver

The initial start of the neutron OVS agent always prints
a warning:

 WARNING stevedore.named [] Could not load
 neutron.agent.linux.iptables_firewall.OVSHybridIptablesFirewallDriver

There's an alias for that in setup.cfg called
iptables_hybrid that would avoid it.

Change-Id: I3f5bf782f4f27dc123e462e494741a8a941641ec
diff --git a/lib/neutron_plugins/ovs_base b/lib/neutron_plugins/ovs_base
index 3cd6c85..baf7d7f 100644
--- a/lib/neutron_plugins/ovs_base
+++ b/lib/neutron_plugins/ovs_base
@@ -83,10 +83,10 @@
 
 function _neutron_ovs_base_configure_firewall_driver {
     if [[ "$Q_USE_SECGROUP" == "True" ]]; then
-        iniset /$Q_PLUGIN_CONF_FILE securitygroup firewall_driver neutron.agent.linux.iptables_firewall.OVSHybridIptablesFirewallDriver
+        iniset /$Q_PLUGIN_CONF_FILE securitygroup firewall_driver iptables_hybrid
         enable_kernel_bridge_firewall
     else
-        iniset /$Q_PLUGIN_CONF_FILE securitygroup firewall_driver neutron.agent.firewall.NoopFirewallDriver
+        iniset /$Q_PLUGIN_CONF_FILE securitygroup firewall_driver noop
     fi
 }