[Openstack-stable-maint] Patch https://review.openstack.org/#/c/17036/

Hi, There is valid concern about the upgrade procedure with this patch. There is a way that we are able to do this without creating an major problems: 1. Leave the class QuantumLinuxBridgeVIFDriver unchanged 2. Add in a new class QuantumLinuxBridgeVIFDriverEnhanced (or if someone has a better name). This class will contain the changes. If someone wants to benefit fro the changes then she/he will need to update their configuration file to:

libvirt_vif_driver=nova.virt.libvirt.vif.QuantumLinuxBridgeVIFDriverEnhanced This can be documented and it may treat all of the concerns. Naturally a patch upstream will need to be added so that this wil be forward compatible. Thoughts? Thanks Gary