[enh] #668: return exit values on daemon status:

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

bin/daemon

@@ -20,10 +20,11 @@ switch (process.argv[2]) {
   case "status":
     if (daemon.status()) {
       console.log('Duniter daemon status: running');
+      process.exit(0)
     } else {
       console.log('Duniter daemon status: stopped');
+      process.exit(2)
     }
-    break;
 
   case "sync":
   case "reset":