Find configuration files on the system.
        :return:

def find_existing_configs(self, default):
        '''
        Find configuration files on the system.
        :return:
        '''
        configs = []
        for cfg in [default, self._config_filename_, 'minion', 'proxy', 'cloud', 'spm']:
            if not cfg:
                continue
            config_path = self.get_config_file_path(cfg)
            if os.path.exists(config_path):
                configs.append(cfg)

        if default and default not in configs:
            raise SystemExit('Unknown configuration unit: {}'.format(default))

        return configs