Use partition devices, not whole disk devices

[octylFractal]

This generates with each partition set as an offset into the device of the entire drive, where as when doing only some partitions it works better to generate with the partition device.

I may have made no sense, so let me clarify with an example:

# original line
RW 461373440 FLAT "/dev/disk0" 12304892
# new line
RW 461373440 FLAT "/dev/disk0s4" 0

When accessing a disk that is mounted VirtualBox will say ERR_RESOURCE_BUSY, but writing it this way solves that.