mkdos: Drop from image. Use mkfs -t fat

Change-Id: If79f67126e23bea6c8dbb348f075832cd0bf8360
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5107
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

fat: add test script using mkdos, fstorture, fsx.

not fully tested, as fstorture crashes with #15357.

Change-Id: If00368f1287af1d46da38fef4c3943956de1db79
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1867
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>