message: exit with 0 on SIGTERM / SIGINT
  so that the manager / supervisor knows that we're exiting successfully.
diff: @@ -33,7 +33,7 @@ pub fn monitor_signal(handle: &Handle, plugins: Vec<Plugin>) {
  .and_then(|sigterm| {
  sigterm.take(1)
  .for_each(|_| -> Result<(), io::Error> {
  - info!("Received SIGTERM, aborting process");
  + info!("Received SIGTERM, exiting.");
  Ok(())
  })
  .map(|_| libc::SIGTERM)
  @@ -47,7 +47,7 @@ pub fn monitor_signal(handle: &Handle, plugins: Vec<Plugin>) {
  .and_then(|sigint| {
  sigint.take(1)
  .for_each(|_| -> Result<(), io::Error> {
  - error!("Received SIGINT, aborting process");
  + info!("Received SIGINT, exiting.");
  Ok(())
  })
  .map(|_| libc::SIGINT)
  @@ -69,8 +69,8 @@ pub fn monitor_signal(handle: &Handle, plugins: Vec<Plugin>) {
  drop(plugins);
  match r {
  - Ok(exit_code) => {
  - process::exit(128 + exit_code);
  + Ok(_signo) => {
  + process::exit(0);
  }
  Err(..) => Err(()),
  }
  