Deprecate old vif drivers.

As per commit 4c0cecd3 (Change-Id I292c2fd7aa0c32b1c91d737152ed8e54ea2cf6ac)
Deprecate:
* LibvirtBridgeDriver
* LibvirtOpenVswitchDriver
* LibvirtHybridOVSBridgeDriver
* LibvirtOpenVswitchVirtualPortDriver
* QuantumLinuxBridgeVIFDriver

Change-Id: Iad854dfe91aaa18622f78aa92746d3ea2f986960
Merge "Deprecate old vif drivers."