How to use Redlock in cluster

Hi @antirez,

At present, many companies use redis cluster to cache data or do other things. If these companies want to use the RedLock algorithm to implement distributed locks, they must create additional and independent redis nodes just for the Redlock. Because the Redlock algorithm assumes the nodes is independent. As quoted below.

> In the distributed version of the algorithm we assume we have N Redis masters. Those nodes are totally independent, so we don’t use replication or any other implicit coordination system.

It is a waste to do that and it's better for us to reuse the cluster. This [link](https://github.com/redisson/redisson/issues/956#issue-241460677) provides more information about this problem.

Do you have any ideas about it?
Thanks.