libtool generates horrible shell code, you don't want to see the
shellcheck results for it ;-)
This is only relevant for local testing (not in CI) because these files
don't exist in git and therefore don't exist when the shellcheck CI job
runs.
- Assume /bin/sh has dash's features and ignore corresponding false positives
- Exclude parser/tst, tests and utils/test directories: they have tons
of shellcheck violations but they don't *directly* impact our users.
Let's first focus on code that runs on production systems.
- Exclude rc.apparmor.slackware: I don't know anything about Slackware's
/bin/sh.
