Adds support for the Indigo Virtual Switch (IVS)

Implements: blueprint ivs-vif-driver

Adds line to rootwrap config to allow call to ivs-ctl to control the Indigo switch.
Adds a new 'ivs' VIF type in network/model.py.
Adds support to the LibvirtGenericVIFDriver class for the IVS switch.
Adds functions to linux_net.py to create and delete IVS vif ports.
Adds unit tests to test the new IVS methods.

Change-Id: I65436b82f65374103644af8aba9dba14ba73f94c
Merge "Adds support for the Indigo Virtual Switch (IVS)"