Fontbakery now exits with error status on FAILs

[simoncozens]

Fontbakery now exits with an error code of the highest check status:

sys.exit(check_profile_main(module.profile))

This action interprets that as a crash, and causes the workflow to fail. font-bakery should capture and interpret the process exit status. I recommend using it to send a warning to the action log file.