Parse the content written by the script to standard err.

        :param filelike: filelike object of stderr
        :returns: an exit code in case of an error, None otherwise

def parse_stderr(self, filelike):
        """Parse the content written by the script to standard err.

        :param filelike: filelike object of stderr
        :returns: an exit code in case of an error, None otherwise
        """
        marker_error = 'ERROR,'
        marker_warning = 'WARNING,'

        messages = {'errors': [], 'warnings': []}

        for line in filelike.readlines():
            if marker_error in line:
                messages['errors'].append(line.split(marker_error)[-1].strip())
            if marker_warning in line:
                messages['warnings'].append(line.split(marker_warning)[-1].strip())

        if self.node.get_option('attach_messages'):
            self.out('messages', Dict(dict=messages))

        for error in messages['errors']:
            if 'unknown option' in error:
                return self.exit_codes.ERROR_INVALID_COMMAND_LINE_OPTION

        return