Parses configuration files from various levels
        and loads configuration.

def parse_config_files(self, filenames=None, ignore_option_errors=False):
        """Parses configuration files from various levels
        and loads configuration.

        """
        self._parse_config_files(filenames=filenames)

        parse_configuration(self, self.command_options,
                            ignore_option_errors=ignore_option_errors)
        self._finalize_requires()