public void setClusterState(State s) {
        if (!s.validClusterState()) {
            throw new IllegalArgumentException("Illegal cluster state " + s);
        }
        state = s;
    }
Sets the state of this cluster state. In particular, it does not set the cluster state,
no matter what the function name says.
vdslib/src/main/java/com/yahoo/vdslib/state/ClusterState.java