public ApplicationInstanceReference toApplicationInstanceReference(ApplicationId applicationId) {
        return ApplicationInstanceGenerator.toApplicationInstanceReference(applicationId, zone);
    }
Make an application instance that contains all services and clusters present on the host,
but lacking other services and hosts. This is an optimization over
{@link #toApplicationInstance(ApplicationInfo, ServiceStatusProvider)}.
service-monitor/src/main/java/com/yahoo/vespa/service/model/ModelGenerator.java