Configure OVS Agent when using ML2 plugin

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.

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Change-Id: Id70420a871edc352f80c0446e89dbcde94e5c490