private Map<ClusterSpec.Id, NodeList> nodesByCluster(NodeList applicationNodes) {
        return applicationNodes.groupingBy(n -> n.allocation().get().membership().cluster().id());
    }
Maintainer computing scaling suggestions for all clusters

@author bratseth
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/ScalingSuggestionsMaintainer.java