qemu: fix hot unplug of PCI devices with VFIO

qemu: fix hot unplug of PCI devices with VFIO

Currently, on hot unplug of PCI devices with VFIO driver for QEMU, libvirt is
trying to restore the host devices to it's previous value (basically a chown
on the previous user/group).

However for devices with VFIO driver, when the device is unbinded it is
removed from the /dev/vfio file system causing the restore label to fail.

The fix is to not restore the label for those PCI devices since they are going
to be teared down anyway.

Signed-off-by: Ludovic Beliveau <ludovic.beliveau@windriver.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>