This adds support for host device passthrough with the
LXC driver. Since there is only a single kernel image,
it doesn't make sense to pass through PCI devices, but
USB devices are fine. For the latter we merely need to
make the /dev/bus/usb/NNN/MMM character device exist
in the container's /dev
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>