WIP - Configure OVS Agent in ML2 config

When running ML2 plugin, Neutron does not read the OVS plugin
configuration file, so the Agents can't work (mount tunnels, configure
L2, etc).
To make it work, you need to move the configuration in ML2 configuration
file.

Currently, neutron::agents::ovs is only able to configure OVS
configuration file. This patch aims to discuss about a new design of the
agents and find a way to keep backward compatibility with old model
(without ML2).

DO NOT MERGE IT.
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

Change-Id: Id70420a871edc352f80c0446e89dbcde94e5c490
fix ovsml2