code: function createHttpErr(statusCode, opts, req) {
      assert.number(statusCode, 'statusCode');
      assert.object(opts, 'opts');
      assert.object(req, 'req');
  
      var errInfo = createErrInfo(opts, req);
  
      return restifyErrors.makeErrFromCode(statusCode, {
          info: errInfo
      });
  }
docs: build an http error for a request that has a corresponding http status code
  on the response.
  @private
  @function createHttpErr
  @param {Object} statusCode response status code
  @param {Object} opts options object for a request
  @param {Object} req the request object
  @returns {verror.VError}