mark vif_driver as deprecated and log warning

Several classes were dropped from nova.virt.libvirt.vif from havana ->
icehouse, leading to invalid configurations if one of these classes was
used in the libvirt_vif_driver setting in nova.conf.  The error message
produced by nova-compute in this situation is misleading.

This patch introduces stubs for all of the classes that were removed.
These stubs inherit from LibvirtGenericVIFDriver and log a deprecation
warning in __init__.

This patch also marks the vif_driver option as deprecated.

Change-Id: I6d6cb9315ce6f3b33d17756bcdc77dccda26fefe
Closed-bug: 1302796
Merge "mark vif_driver as deprecated and log warning"