[enh] return exit values on daemon status

Created by: M5oul

#668 (closed):

• https://nodejs.org/api/process.html#process_exit_codes
• this will allow me to partially fix:
  • https://github.com/YunoHost-Apps/duniter_ynh/issues/21
  • stop daemon will only be done when daemon running.

duniter stop
echo $?
2
duniter start
echo $?
0