Changed get_epoch_time_for_grafana method so that it can accept a start time and end time, but if one is not specified, it defaults to the start/end time (respectively) for the reporting time period
Changed get_epoch_time_for_grafana method so that it can accept a start time and end time, but if one is not specified, it defaults to the start/end time (respectively) for the reporting time period

shreyb/gracc-reporting,shreyb/gracc-reporting