Adds support for the Indigo Virtual Switch

Allows users to specify which virtual switch Quantum should use
and inform Nova to use. It configures the quantum dhcp agent
interface driver to bind to the correct switch and sets the
vif_type that the BigSwitch/Floodlight plugin will send to Nova.

Change-Id: I077a9ce8ab205e2949e0a438307f7da46a8a247d
Implements: blueprint ivs-support
Merge "Adds support for the Indigo Virtual Switch"