message: print errno if daemonize failed
diff: @@ -14,6 +14,6 @@ pub fn daemonize<F: AsRef<Path>>(pid_path: Option<F>) {
  }
  if let Err(err) = d.start() {
  - error!("failed to daemonize, {}", err);
  + error!("failed to daemonize, {:?} ({})", err, err);
  }
  }
  