terminate process and wipe out the temp work directory, but only if we actually started it

def stop(self, kill=False, timeout=15):
        """ terminate process and wipe out the temp work directory, but only if we actually started it"""
        super(AbstractDcsController, self).stop(kill=kill, timeout=timeout)
        if self._work_directory:
            shutil.rmtree(self._work_directory)