Cluster: Tcl cluster client: get nodes description.
Cluster: Tcl cluster client: build nodes representation.
Cluster: Tcl cluster client: slots-nodes map and close method.

Now the client is able to actually run commands in a Redis Cluster
assuming the slots->nodes map is stable.
Cluster: Tcl cluster client: handle MOVED/ASK.
Test: cluster/base, check that we can write/read from cluster.