A new Devstack setting was recently introduced[1] for OVN
OVN_BUILD_FROM_SOURCE allowing to use the packaged
version when set to False. The value of OVS_RUNDIR
changes accordingly that setting, so we needs to make sure
ovs will always run on same path to avoid database
connection failures.
[1] https://github.com/openstack/devstack/
commit/e651d9ef8840bb7dd497b557125ce1cd5290993d
Change-Id: I3a7b7dcd46cb5efa747d72517b5c26560db698af
c68a6fe1e7