def start_and_end_times(self):
        return [(x.node_monitor_launch_time, x.completion_time) for x in self.__tasks.values()
                if x.complete()]
Returns a list of (launch time, finish time) tupes for complete __tasks. Ignores
dataset/ETHPy150Open radlab/sparrow/src/main/python/parse_logs.py/Request.start_and_end_times