code: function version(cb) {
  
    function _cb(err, result, response) {
      if (err) {
        cb(err);
      } else if (response.headers['x-jenkins']) {
        cb(null, response.headers['x-jenkins']);
      } else {
        cb(new Error(text.__('Not a Jenkins server')));
      }
    }
    this.remoteAccessApi.headJenkins(_cb);
  }
docs: Retrieve Jenkins version number from x-jenkins header.
  If x-jenkins header does not exist, then it's assumed that the server is not a Jenkins instance.
  
  @param {Function} cb: standard cb(err, result) callback