vmm/virtualbox: Update for VirtualBox 3.0
vmm/virtualbox: Update for VirtualBox 3.0

- Pass additional arguments to openHardDisk()

- Use forgetSavedState() or discardSavedState() depending on the VBox
version.  Only rename the state file out of the way beforehand if using
discardSavedState().

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