bug#41235: guix deploy can't deploy with a user different than root

[Brice Waegeneire <brice@waegenei.re>]

Hello,

When trying to reproduce another “guix deploy” bug for a future bug 
report
I stumbled upon this one: it's not possible to deploy as a user
(machine-ssh-configuration-user) different than “root“, even with a
properly configured sudoers file[0]. Deploying with root works when ssh 
is
configured with “PermitRootLogin yes”. Following is the backtrace:

--8<---------------cut here---------------start------------->8---
$ guix deploy -Lmodules systems/hystou-p04.scm
guix deploy: warning: failed to load '(config workstation)':
no code for module (gnu services lightdm)
The following 1 machine will be deployed:
   abricot

guix deploy: deploying to abricot...
sending 0 store items (0 MiB) to '192.168.10.10'...
Backtrace:
In guix/ui.scm:
   1936:12 19 (run-guix-command _ . _)
In guix/status.scm:
     776:4 18 (call-with-status-report _ _)
In ice-9/boot-9.scm:
   1736:10 17 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
    630:22 16 (thunk)
    1295:8 15 (call-with-build-handler _ _)
    1295:8 14 (call-with-build-handler #<procedure 7fe8ee3bc120 at g…> …)
In guix/scripts/deploy.scm:
    155:12 13 (_)
In guix/store.scm:
    1336:2 12 (map/accumulate-builds #<store-connection 256.99 7fe8e…> …)
In srfi/srfi-1.scm:
    586:17 11 (map1 (#<<unresolved> things: (("/gnu/store/x32cnfkd50…>))
In guix/store.scm:
    1295:8 10 (call-with-build-handler #<procedure build-accumulator…> …)
In guix/scripts/deploy.scm:
     123:2  9 (_ _)
In ice-9/boot-9.scm:
   1736:10  8 (with-exception-handler _ _ #:unwind? _ # _)
In guix/scripts/deploy.scm:
     133:4  7 (_)
In guix/store.scm:
   2015:24  6 (run-with-store #<store-connection 256.99 7fe8ee3a75f0> …)
In gnu/machine/ssh.scm:
     416:2  5 (_ _)
     316:2  4 (_ _)
In guix/remote.scm:
    138:10  3 (_ _)
In guix/store.scm:
   1886:38  2 (_ #<store-connection 256.99 7fe8ee7dba50>)
In ice-9/boot-9.scm:
   1669:16  1 (raise-exception _ #:continuable? _)
   1667:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1667:16: In procedure raise-exception:
ERROR:
   1. &store-protocol-error:
       message: "unknown error while sending files over SSH"
       status: 44
--8<---------------cut here---------------end--------------->8---

[0]: 
https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix-deploy.html#Invoking-guix-deploy

- Brice