Formats the image with an MBR partition table

[hufman]

Tested by booting the image as a harddisk image in qemu

[jirutka]

Partitions are completely unnecessary in VMs, it doesn’t make any sense to use them in this environment. I know that there are some cloud providers with a broken setup that foolishly require a partition table – the users should first complain there, not require adding an unnecessary feature into this script.

However, I’m a realist, so I’m not against adding this support but only as an alternative to the current approach (i.e. a new CLI option), not as a replacement.