Add Neutron l3 metering agent
Add Neutron l3 metering agent

This is the agent side of :
blueprint bandwidth-router-measurement
blueprint bandwidth-router-label

This patch initiates agent side by adding a new
l3 metering agent and a Noop Driver.

DocImpact

Change-Id: Ib34721209c282b2669ff5488a33293d9f86467ef

dougwig/x-neutron-fwaas,citrix-openstack-build/neutron-fwaas,openstack/neutron-fwaas,openstack/neutron-fwaas,gaolichuang/neutron-fwaas,gaolichuang/neutron-fwaas