uvol: update to re-write in ucode

uvol: update to re-write in ucode

Replace previous Shell draft-quality implementation of uvol with a
rewrite in ucode[1].
While the new code is slightly larger, it performs much better (as
we no longer fork() for parsing strings like in Shell with grep, sed
and friends).

Before:
  time uvol list -j
  [ ... ]
  real	0m 0.82s
  user	0m 0.13s
  sys	0m 0.10s

After:
  time uvol list -j
  [ ... ]
  real	0m 0.47s
  user	0m 0.05s
  sys	0m 0.05s

[1]: https://github.com/jow-/ucode
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 6350c7bc63a1cf32e4ef9de42d2e47983df25932)