Merge QuantumLinuxBridgeVIFDriver into LibvirtGenericVIFDriver

The only difference between the Quantum bridge driver and the
new generic VIF driver bridge support is the name of the bridge.
This is now provided via the VIF mapping parameter, so there is
no need for the dedicated Quantum VIF driver for bridging. This
This has the advantage that libvirt firewall filter parameters
are correctly configured.

The QuantumLinuxBridgeVIFDriver class functionality is merged into
LibvirtGenericVIFDriver. For backwards compatibility with
the Folsom release, the existing QuantumLinuxBridgeVIFDriver class
is made to inherit from LibvirtGenericVIFDriver and directly
call the bridge specific setup APIs. This eases migration to
the new VIF impl during the Grizzly deployment lifecycle, with
an expectation that the QuantumLinuxBridgeVIFDriver stub will be
deleted after the Havana release.

Blueprint: libvirt-vif-driver
Change-Id: I19664f20e5137f495513999214f66279292bda58
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Merge "Merge QuantumLinuxBridgeVIFDriver into LibvirtGenericVIFDriver"