Handle ovs_use_veth option

Change-Id: I3331ddae9840d9b1ae3dc07e4065684fbb1ab15f
Closes-Bug: PROD-21373
diff --git a/tests/pillar/gateway_legacy.sls b/tests/pillar/gateway_legacy.sls
index c67c80b..c2606f3 100644
--- a/tests/pillar/gateway_legacy.sls
+++ b/tests/pillar/gateway_legacy.sls
@@ -3,6 +3,7 @@
     agent_mode: legacy
     dhcp_lease_duration: 86400
     firewall_driver: noop
+    ovs_use_veth: True
     backend:
       engine: ml2
       tenant_network_types: "flat,vxlan"