Enable Firewall as a Service plugin

Aims to enable FWaaS plugin when using Neutron in the gate.
It will allow us to run Tempest tests against devstack-gate.

Change-Id: Iaf751730554c226a750d4deea61d7011a180d669
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "Enable Firewall as a Service plugin"