The LXC controller is closing loop devices as soon as the
container has started. This is fine if the loop device
was setup as a mounted filesystem, but if we're just passing
through the loop device as a disk, nothing else is keeping
it open. Thus we must keep the loop device FDs open for as
long the libvirt_lxc process is running.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>