tempest: set network-feature-enabled.port_security

Sets the port_security feature flag in tempest.conf
if the port_security extension is enabled, which it's not
by default in neutron but is set by default in devstack.

This adds global variable for setting the port_security
extension in ml2.conf and in tempest.conf so we only have
to set this in one place.

Depends-On: I1efd5c838aa0d73cc6e8864e3041eea25850198d

Change-Id: I6334b200e42edd785f74cfb41520627393039619
Related-Bug: #1624082
diff --git a/lib/neutron_plugins/ml2 b/lib/neutron_plugins/ml2
index 7e80209..e429714 100644
--- a/lib/neutron_plugins/ml2
+++ b/lib/neutron_plugins/ml2
@@ -35,7 +35,11 @@
 Q_ML2_PLUGIN_GENEVE_TYPE_OPTIONS=${Q_ML2_PLUGIN_GENEVE_TYPE_OPTIONS:-vni_ranges=$TENANT_TUNNEL_RANGES}
 # List of extension drivers to load, use '-' instead of ':-' to allow people to
 # explicitly override this to blank
-Q_ML2_PLUGIN_EXT_DRIVERS=${Q_ML2_PLUGIN_EXT_DRIVERS-port_security}
+if [[ "$NEUTRON_PORT_SECURITY" = "True" ]]; then
+    Q_ML2_PLUGIN_EXT_DRIVERS=${Q_ML2_PLUGIN_EXT_DRIVERS-port_security}
+else
+    Q_ML2_PLUGIN_EXT_DRIVERS=${Q_ML2_PLUGIN_EXT_DRIVERS:-}
+fi
 
 # L3 Plugin to load for ML2
 # For some flat network environment, they not want to extend L3 plugin.