PCI passthrough Libvirt vm config

PCI passthrough device's xml config formatter. adding pci
passthrough device to VM, and detach it from a VM. adapter the
hypervisor PCI passthrough devices management interface given a
unify interface to other PCI passthrough components.

bp:pci-passthrough-libvirt

Co-authored-by: Boris Pavlovic <boris@pavlovic.me>
Change-Id: If55648e5cc2ed5b7ea44aad08205689d99338856
Signed-off-by: Yongli He <yongli.he@intel.com>
Merge "PCI passthrough Libvirt vm config"