code: def _time_query_parms(begin_time, end_time):
          
          query_parms = []
          if begin_time is not None:
              begin_ts = timestamp_from_datetime(begin_time)
              qp = 'begin-time={}'.format(begin_ts)
              query_parms.append(qp)
          if end_time is not None:
              end_ts = timestamp_from_datetime(end_time)
              qp = 'end-time={}'.format(end_ts)
              query_parms.append(qp)
          query_parms_str = '&'.join(query_parms)
          if query_parms_str:
              query_parms_str = '?' + query_parms_str
          return query_parms_str
docs: Return the URI query paramterer string for the specified begin time
          and end time.