private long countStatus(List<ServerGroup.Server> upstreams, boolean up) {
        return upstreams.stream().filter(nginxServer -> up == nginxServer.up()).count();
    }
Report Nginx metrics periodically.

@author Morten Tokle
@author Martin Polden
routing-generator/src/main/java/com/yahoo/vespa/hosted/routing/nginx/NginxMetricsReporter.java