message: [build_exception] Decode build failure messages
  This is so that the test harness pretty-prints build error messages in
  trace mode, instead of dumping a raw python bytes object.
diff: @@ -13,4 +13,4 @@ class BuildError(Exception):
  @staticmethod
  def format_build_error(command, command_output):
  return "Error when building test subject.\n\nBuild Command:\n{}\n\nBuild Command Output:\n{}".format(
  - command, command_output)
  + command, command_output.decode("utf-8"))
  