Setup logging via ini-file from logging_conf_file option.

def _conf(cls, opts):
        """Setup logging via ini-file from logging_conf_file option."""
        if not opts.logging_conf_file:
            return False

        if not os.path.exists(opts.logging_conf_file):
            # FileNotFoundError added only in Python 3.3
            # https://docs.python.org/3/whatsnew/3.3.html#pep-3151-reworking-the-os-and-io-exception-hierarchy
            raise OSError("Error: Unable to locate specified logging configuration file!")

        logging.config.fileConfig(opts.logging_conf_file, disable_existing_loggers=False)
        return True