`man 1 sh` says about '-e':
```
The shell does not exit if the command that fails is part of the command list
immediately following a while or until keyword, part of the test following
the if or elif reserved words, part of any command executed in a && or || list
except the command following the final && or ||, any command in a pipeline
but the last, or if the command's return value is being inverted with !.

That's why testing error handling in the functional tests didn't check
the exit status at all :(

Let's fix that.
Example before the fix:
! coverage run -a --branch bin/kconfig-hardened-check -l /proc/cmdline
Example after the fix:
coverage run -a --branch bin/kconfig-hardened-check -l /proc/cmdline && exit 1