very simple read repeater, when gets error, try repeat after 500ms, but max 5 times
@param {String} filePath
@param {Function} callback(err, data)
function readFile(filePath, opts, callback, count){ // callback(err)
    if(arguments.length===2){
        callback = arguments[1];
        opts = null;
    }
    if(typeof callback !== 'function') throw new Error('Wrong arguments');
    
    filePath = path.resolve(filePath);
    count = count || 0;
    var maxLimit = 5; // 5 * 500ms = 2,5s
    
    fs.readFile(filePath, opts, function(err, data) {
        if(err) {
            if(count >= maxLimit) callback(new Error('fsExt.readFie: max repeat limit reached').cause(err)); // repeat limit reached
            else setTimeout(function(){
                readFile(filePath, opts, callback, count + 1);
            }, 500);
        }
        else callback(null, data);
    });
}