Currently when OVS-DPDK is enabled, instances fail to spawn
due to permissions mismatch, see nova bug for details:
https://bugs.launchpad.net/nova/+bug/1670950
This patch configures OVS to use a separate dir, created by
nova formula [1].
[1] https://gerrit.mcp.mirantis.net/11213
Related-PROD: PROD-14413
Change-Id: Ia86658b0967b4d35f063c7f6f53e26e78a1fbd39