def gather_outputs_from_work_units
      units = self.work_units.complete
      outs = self.work_units.complete.map {|u| u.parsed_output }
      self.work_units.complete.destroy_all
      outs.to_json
    end
def gather_outputs_from_work_units
      units = self.work_units.complete
      outs = self.work_units.complete.map {|u| u.parsed_output }
      self.work_units.complete.destroy_all
      outs.to_json
    end
When the WorkUnits are all finished, gather all their outputs together
 before removing them from the database entirely. Returns their merged JSON.