VMware: Ensure Quantum networking works with VMware drivers

Fixes bug 1202042

A new utility method, is_quantum, is added. This returns True
if Quantum is used by the network_api_class.

(cherry picked from commit 2d7520264a4610068630d7664eeff70fb5e8c681)

Change-Id: Iaf22a43c8e36a7e5825574a082491354e4523619
Merge "VMware: Ensure Quantum networking works with VMware drivers" into cells_grizzly