Remove OVN leftover from the dragonflow devstack plugin
Remove OVN leftover from the dragonflow devstack plugin

OVS build and startup Originally copied from
https://github.com/openstack/networking-ovn/blob/master/devstack/plugin.sh
Change-Id: Ia5d921b0ee1e35c69a5268448de75cb4c0fb123b

openstack/dragonflow,FrankDuan/df_code,FrankDuan/df_code,openstack/dragonflow,FrankDuan/df_code,openstack/dragonflow