def get_motion(self, name):
        try:
            return self._motions[name]
        except KeyError:
            raise UnknownDevice(name)
Parse stderr from the ``hadoop jar`` command. Works like
dataset/ETHPy150Open iancmcc/ouimeaux/ouimeaux/environment.py/Environment.get_motion--crossover with--dataset/ETHPy150Open Yelp/mrjob/mrjob/logs/step.py/_interpret_hadoop_jar_command_stderr