This patch adds the enable-qos option to the charm. If enable-qos is
set then neutron.services.qos.qos_plugin.QoSPlugin is added to
service_plugins in neutron.conf locally. The
neutron-plugin-api-relation has also been updated to send the
enable-qos option to charms connected over that relation (for
example neutron-openvswitch and neutron-gateway).
As part of this some of the logic for setting service_plugins was
removed from the neutron.conf and placed in the NeutronCCContext.
This patch is based on the steps in:
https://docs.openstack.org/mitaka/networking-guide/config-qos.html
Change-Id: I1beba9bebdb7766fd95d47bf13b6f4ad86e762b5
Partial-Bug: #1705358
a8e6824e3a