bug#51728: Incomplete build logs via --log-file (due to offloading?)

[Maxim Cournoyer]

Hello,

I *think* this may be caused by the fact that dbus-test-runner was
probably built in an ad-hoc manner (running guix build on the berlin
machine directly), but I am unsure.  At any rate, the log file it
returns is not helpful:

--8<---------------cut here---------------start------------->8---
$ wget -q -O- $(./pre-inst-env guix build dbus-test-runner --log-file) | zcat
substitute: updating substitutes from 'http://141.80.167.131'... 100.0%
fetching path 
`/gnu/store/3x0nqzc6n955sdzywirwbvssy5qy3g66-dbus-test-runner-19.04.0'...
@ substituter-started 
/gnu/store/3x0nqzc6n955sdzywirwbvssy5qy3g66-dbus-test-runner-19.04.0 substitute
Downloading 
http://141.80.167.131/nar/lzip/3x0nqzc6n955sdzywirwbvssy5qy3g66-dbus-test-runner-19.04.0...
 dbus-test-runner-19.04.0                    136KiB/s 00:01 | 76KiB transferred

@ substituter-succeeded 
/gnu/store/3x0nqzc6n955sdzywirwbvssy5qy3g66-dbus-test-runner-19.04.0
--8<---------------cut here---------------end--------------->8---

That's for dbus-test-runner on the core-updates-frozen-batched-changes
branch.

Thanks,

Maxim