readyCheck(callback) {
        this.cluster("info", function (err, res) {
            if (err) {
                return callback(err);
            }
            if (typeof res !== "string") {
                return callback();
            }
            let state;
            const lines = res.split("\r\n");
            for (let i = 0; i < lines.length; ++i) {
                const parts = lines[i].split(":");
                if (parts[0] === "cluster_state") {
                    state = parts[1];
                    break;
                }
            }
            if (state === "fail") {
                debug$c("cluster state not ok (%s)", state);
                callback(null, state);
            }
            else {
                callback();
            }
        });
    }
Check whether Cluster is able to process commands

@param {Function} callback
@private