* refactored scripts located under `target/bin/`
The scripts under `target/bin/` now use the new log and I replaced some
`""` with `''` on the way. The functionality stays the same, this mostly
style and log.
* corrected fail2ban (script and tests)
* corrected OpenDKIM log output in tests
* reverted (some) changes to `sedfile`
Moreover, a few messages for BATS were streamlined and a regression in
the linting script reverted.
* apple PR feedback
* improve log output from `fail2ban` script
The new output has a single, clear message with the '[ ERROR ] '
prefix, and then output that explains the error afterwards. This is
coherent with the logging style which should be used while providing
more information than just a single line about IPTables not functioning.
* simplified `setquota` script
* consistently named the `__usage` function
Before, scripts located under `target/bin/` were using `usage` or
`__usage`. Now, they're using `__usage` as they should.
* improved `sedfile`
With `sedfile`, we cannot use the helper functions in a nice way because
it is used early in the Dockerfile at a stage where the helper scripts
are not yet copied. The script has been adjusted to be canonical with
all the other scripts under `target/bin/`.
* fixed tests
* removed `__usage` from places where it does not belong
`__usage` is to be used on wrong user input, not on other failures as
well. This was fixed in `delquota` and `setquota`.
* apply PR review feedback
