Neutron-sfc-agent start its functions with openvswitch.
This change moves sfc configuration into neutron-openvswitch-agent.
Rework config files to use openvswitch when sfc or openvswitch
are used as network plugin.
Also adds sfc extension_driver to ml2
Change-Id: If1ebf9554f6d686cc6d064e698a48f8a6b6172b3
Closes-Bug: #1664493
Depends-On: I60ba1333231a4ae38a041d41e551f7d74fe15e3b