installer: Fix configuration edition during testing....When the configuration is edited, it looks like there are some leftover
fragments from the input configuration:
Example content of config.scm after edition:
#:imported-modules
'((gnu services herd)
(guix build utils)
(guix combinators)))
unted". The unique
;; file system identifiers there ("UUIDs") can be obtained
;; by running 'blkid' in a terminal.
...
This is strange because call-with-output-file uses the O_TRUNC flag which
resets the file size to zero. Remove the configuration file before writing it
as a work-around.
* gnu/installer/tests.scm (edit-configuration-file): Remove the configuration
file before re-writing it.