public void shutdown() {
        if (fileAcquirer != null)
            fileAcquirer.shutdown();
        if (urlDownloader != null)
            urlDownloader.shutdown();
    }
The container instance. This is a Vespa internal object, external code should
only depend on this if there are no other options, and must be prepared to
see it change at no warning.

@author bratseth
container-core/src/main/java/com/yahoo/container/Container.java