private String getHostnamePrefix() {
        int dotIndex = hostName.s().indexOf('.');
        return dotIndex == -1 ? hostName().s() : hostName.s().substring(0, dotIndex);
    }
Get a name that can be used in e.g. config server logs that makes it easy to understand which
service instance this is.
application-model/src/main/java/com/yahoo/vespa/applicationmodel/ServiceInstance.java