cluster: make ForEachNode iterate through each node

[gbbr]

ForEachNode was iterating through the masters and slaves fields,
which are the result of the addresses advertised by the cluster, but do
not contain the addresses used to create the cluster (in
ClusterOptions). This was problematic in some situations. This PR
addresses that issue.

This might make more sense because it is the nodes property that is used
when selecting nodes, not masters and slaves. (see here).

This addresses #701. If you decide against making this change, please
feel free to close the PR.

[vmihailenco]

I need to think about this, but I am not comfortable that with this change ForEachMaster+ForEachSlave != ForEachNode.

[gbbr]

No problem, take your time. You have the context knowledge.

The way I thought of it was that ForEachMaster and ForEachSlave would iterate through the cluster advertised masters and slaves, while ForEachNode would iterate through all nodes including the ones used at startup time.

Either way, if you decide against it, I can work around it but in some situations it could be problematic given our scenario.

Thanks for looking.

[vmihailenco]

After some testing I think it should be ForEachNode = ForEachMaster + ForEachSlave. Otherwise it would require go-redis to keep connection/client to all nodes that ever existed in the cluster which sounds dubious.

[gbbr]

Sure. I can definitely understand your point of view. And I'm ok with it 👍 I think my case is somewhat of an edge-case that should normally not happen in a real life scenario. I suspect my case was one of a misconfigured cluster, where the nodes addresses used with go-redis were different than the ones advertised by the cluster.