function _getConfig(configFileName) {
  const appdir = process.env.PWD || process.cwd();
  const custom_config_filename = path.join(appdir, configFileName);
  let userConfig = {};

  if (fileExists(custom_config_filename)) {
    userConfig = fs.readFileSync(custom_config_filename, {
      encoding: "utf8",
    });
    userConfig = JSON.parse(userConfig);
  } else {
    //console.warn('Could not find configuration file at ' + custom_config_filename);
  }
  return userConfig;
}
Build a path from current process working directory (i.e. meteor project
root) and specified file name, try to get the file and parse its content.
@param configFileName
@returns {{}}
@private