Comment 8 for bug 1671804

In the diff http://paste.openstack.org/raw/603161/ you can see the last line says: "run_as_root=True" which should eventually prefix the command with rootwrap helper or daemon.

Is root_helper_daemon configured on the node (in the neutron.conf or openvswitch_agent.ini)?
Can you please enable debug logs and attach full agent log?