Add metering agent support

The Ceilometer project is able to get meters from Neutron via the
notifications system on how much bandwidth the projects are using.
The idea is to meter this as the L3 routers levels.

The feature exists since Havana.

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
implement blueprint metering-agent

Change-Id: I62ad9b7455e5f2bc3455b55a346f2515ca1040a3
Merge "Add metering agent support"