vmm/virtualbox: Automatically bind $CFGDIR/virtualbox.iso to the machine
vmm/virtualbox: Automatically bind $CFGDIR/virtualbox.iso to the machine

- If $CFGDIR/virtualbox.iso exists, register it and mount it on the
machine's DVD drive at resume time, and unregister it at suspend.  We
don't explicitly unmount the medium because on >= 3.1 we remove the
entire DVD drive at shutdown, and on 3.0 the attached medium will be
deleted from the machine XML at next resume.

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr