Wait for a proc to shut down, then terminate or kill it after `timeout`.

def _shutdown_proc(p, timeout):
  """Wait for a proc to shut down, then terminate or kill it after `timeout`."""
  freq = 10  # how often to check per second
  for _ in range(1 + timeout * freq):
    ret = p.poll()
    if ret is not None:
      logging.info("Shutdown gracefully.")
      return ret
    time.sleep(1 / freq)
  logging.warning("Killing the process.")
  p.kill()
  return p.wait()