getSerialCallback = function (fns) {
    if (!fns.length) {
        return null;
    }
    return function (callback) {
        var that = this;
        var bound_fns = [];
        for (var i = 0, len = fns.length; i < len; i++) {
            (function (j) {
                bound_fns.push(function () {
                    return fns[j].apply(that, arguments);
                });
            })(i);
        }
        return async.series(bound_fns, callback);
    };
}
Returns a serial callback from two functions.

@param {Function} funcFirst
@param {Function} funcSecond
@api private