Switch VIF driver to Generic

The LibvirtHybridOVSBridgeDriver was deprecated in Havana and
removed entirely in Icehouse.  However, it's still the default
VIF driver in puppet_openstack_builder.  This patch changes it
to use the LibvirtGenericVIFDriver instead (and removes the
now-unnecessary reference to Quantum since we have proper stable
branches now).

Change-Id: I037fefd348c20c6576c40e321ea556a7cb05c791
Closes-Bug: #1302082
Merge "Switch VIF driver to Generic"