[libvirt] separate module for pci passthrough device assigning and in-use tracking

Hi, Shradha, Laine Some time before I found you had a thread discussing in-use tracking for network and pci-passthrough devices[1], it mentioned code for tracking pci device allocation should be better as a separate module rather than a part of qemu, so that it could solve data sharing problem between hypervisor drivers and network driver. And after that, we wanted to add pci passthrough support to libxl driver[2], which turned to be the same problem, data sharing between libxl driver and other drivers, and there were code duplication between libxl and qemu driver. Laine suggested again to write code in common library as a separate module. Now I wonder if there is anyone already worked and pushed this thing to some status? If not, I am willing to try it. Thanks, Chunyan