vmm/virtualbox: Default to "Save machine state" when stopping new VMs
vmm/virtualbox: Default to "Save machine state" when stopping new VMs

- Configure newly-created VMs so that the default option when exiting
VirtualBox after the first resume is "Save the machine state" rather
than "Send the shutdown signal"

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