message: Set "deterministic=True" when serializaing to a string in key_util.
diff: @@ -230,7 +230,7 @@ def _normalize_and_text_format_message(msg: message.Message,
  # solution in Tink, or else the proto team provides us with a reflection
  # based API to do this (as they do in C++.) In this case, we simply use the
  # slow API here.
  - value = field_proto.SerializeToString()
  + value = field_proto.SerializeToString(deterministic=True)
  setattr(msg, 'value', value)
  output.append(
  _text_format_field(value, fields[1], indent))
  