L3 API support for BigSwitch-FloodLight Plugin

In keeping with the philosophy  of the RESTProxy plugin, L3 extension calls
are processed (CRUD of logical resources) and the state changes are proxied
to a backend controller.

A configuration variable specific to the RESTProxy plugin is being added
to identify that particular Quantum server's ID.

blueprint quantum-floodlight-bigswitch-l3

Change-Id: I24be02cd836352497fe5b1e7622d138e0c816377