Generate device.map from vm config

[jbergstroem]

Instead of creating a device.map it could be generated from devices in a vm config, then written into a temporary file removed after grub-bhyve is done. Parsing type would allow figuring out type (hd,cd). I guess name could be optionally provided is order is essential (otherwise top down ordering).

[jbergstroem]

My suggested plan is to parse device type and use hdN for for virtio-blk, ahci-hd and cdN for ahci-cd. I'll just add them to device.map in order of appearance, same goes for numbering.

[allanjude]

We added a -b flag, to select the boot device. You might want to make that device be first.

[jbergstroem]

@allanjude sure, I'll have that in mind.

[jbergstroem]

Since bhyveucl -b would conflict with input_args.root passed to grub-bhyve (essentially the same thing), I don't think it sould be relevant when generating device.map or modifying the input to grub-bhyve.