bug#32855: sshuttle /usr/bin/env

[Nam Nguyen]

Hi Tobias,

After testing, I think the /bin/sh substitution introduced a regression.

Lines in question:
(substitute* "sshuttle/ssh.py"
  ;; Perhaps this is unreachable, but don't let's take risks.
  (("/bin/sh") (which "sh")))

$ sshuttle -r user <at> server.com 0/0 -x server.com
ksh: /gnu/store/rb...-bash-minimal-4.4.19/bin/sh: not found
client: fatal: server died with error code 127

The server I am sshing to is not running GuixSD. It is trying to find
/gnu/store/.../bin/sh but it doesn't exst. My local client is running
GuixSD. The only requirements on the server side should be Python. Should
those lines should be removed? I tested without, and it seems to work okay,
at least for my particular setup: GuixSD client --> non-GuixSD server.

I suppose we have to state the assumptions of whether the client and
server are running Guix or not, and arrive at good defaults.