bug#22797: Using UUID for vfat file system is impossible

[Alex Kost]

Hello, unlike other file system types, FAT volumes have short UUIDs,
for example: "58D7-4FA5", but such an UUID cannot be used in an
operating system declaration:

(file-system
  (device (uuid "58D7-4FA5"))
  (title 'uuid)
  (type "vfat")
  ;; ...
  )

because (uuid "58D7-4FA5") errors.

-- 
Alex