code: def scheduling_block_instances(self):
          
          # TODO(BMo) change this to a pipe?
          sbi_list = SchedulingBlockInstanceList()
          return json.dumps(dict(active=sbi_list.active,
                                 completed=sbi_list.completed,
                                 aborted=sbi_list.aborted))
docs: Return the a JSON dict encoding the SBIs known to SDP.