Unhardcode more options for dhcp agent

Change-Id: I4e0ff6f5a77a012d5e2bd5d52a24e3574bf98df9
diff --git a/tests/pillar/gateway_legacy.sls b/tests/pillar/gateway_legacy.sls
index c2606f3..5776d69 100644
--- a/tests/pillar/gateway_legacy.sls
+++ b/tests/pillar/gateway_legacy.sls
@@ -3,7 +3,6 @@
     agent_mode: legacy
     dhcp_lease_duration: 86400
     firewall_driver: noop
-    ovs_use_veth: True
     backend:
       engine: ml2
       tenant_network_types: "flat,vxlan"
@@ -26,3 +25,6 @@
       password: password
       workers: 2
     version: mitaka
+    agents:
+      dhcp:
+        ovs_use_veth: True