Change default network backend driver to ML2/OVN

This patch is changing the default network backend driver in DevStack to
OVN.

This is a long effort from the Neutron community that has been
discussed on previous PTGs and agreed upon.

A similar patch to this one [0] have been merged in the past but got
reverted [1] because it did break some zuul jobs. This one also include
fixes for such jobs and was verified at [2]

[0] https://review.opendev.org/c/openstack/devstack/+/735097
[1] https://review.opendev.org/c/openstack/neutron/+/775632
[2] https://review.opendev.org/c/zuul/zuul-jobs/+/791117

Change-Id: I8c2be82f33ed9f6c36f5509b3b210ee1a38e87ca
Signed-off-by: Lucas Alvares Gomes <lucasagomes@gmail.com>
diff --git a/stackrc b/stackrc
index 196f61f..0501659 100644
--- a/stackrc
+++ b/stackrc
@@ -72,8 +72,10 @@
     ENABLED_SERVICES+=,g-api
     # Cinder
     ENABLED_SERVICES+=,c-sch,c-api,c-vol
+    # OVN
+    ENABLED_SERVICES+=,ovn-controller,ovn-northd,ovs-vswitchd,ovsdb-server
     # Neutron
-    ENABLED_SERVICES+=,q-svc,q-dhcp,q-meta,q-agt,q-l3
+    ENABLED_SERVICES+=,q-svc,q-ovn-metadata-agent
     # Dashboard
     ENABLED_SERVICES+=,horizon
     # Additional services