message: Prefix error messages with "error".
diff: @@ -332,7 +332,7 @@ class Drake:
  break
  except Exception as e:
  self.notify(1, str(e), start)
  - print('%s: %s' % (sys.argv[0], e))
  + print('%s: error: %s' % (sys.argv[0], e))
  if env('DEBUG_BACKTRACE') is not None:
  import traceback
  traceback.print_exc()
  