Activate neutron L2 Gateway extension

Disable l2gw agent by default to prevent unwanted connection attempts to
absent hardware switch (will be emulated/enabled by test suite on demand).

Change-Id: Iaf6da1e0f73f474d6eaee2b15e7613d58b129150
Related-Prod: PROD-18748
diff --git a/classes/cluster/virtual-mcp-pike-ovs/openstack/control.yml b/classes/cluster/virtual-mcp-pike-ovs/openstack/control.yml
index 7a4889b..4ab6709 100644
--- a/classes/cluster/virtual-mcp-pike-ovs/openstack/control.yml
+++ b/classes/cluster/virtual-mcp-pike-ovs/openstack/control.yml
@@ -120,6 +120,10 @@
         engine: file
       images: []
       workers: 1
+  neutron:
+    server:
+      l2gw:
+        enabled: true
   nova:
     controller:
       networking: dvr