Stop the subprocess.

        Keyword Arguments

        **timeout**
          Time in seconds to wait for a process and its
          children to exit.

def stop(self, timeout=15):
        """Stop the subprocess.

        Keyword Arguments

        **timeout**
          Time in seconds to wait for a process and its
          children to exit.
        """
        pp = self.pid
        if pp:
            try:
                kill_process_nicely(pp, timeout=timeout)
            except psutil.NoSuchProcess:
                pass