[OVN] Explicitly set grenade job to ML2/OVS
[OVN] Explicitly set grenade job to ML2/OVS

Devstack is changing the Neutron default to OVN backend. For the grenade
job we need to wait until the stable branch is deployed with OVN so that
we can upgrade it to master.

Change-Id: I51f0273e90ee39d644cf85a0bdb9d4f95de6d3c7
Signed-off-by: Lucas Alvares Gomes <ef89b923b1145c9ec2fd96eee513279016a7a963@gmail.com>

mahak/nova,openstack/nova,mahak/nova,openstack/nova,mahak/nova,openstack/nova