Writes flow results for a given flow.

def WriteFlowResults(self, results):
    """Writes flow results for a given flow."""
    for r in results:
      dest = self.flow_results.setdefault((r.client_id, r.flow_id), [])
      to_write = r.Copy()
      to_write.timestamp = rdfvalue.RDFDatetime.Now()
      dest.append(to_write)