private boolean validateResponse(Request request) {
        if (request.isError()) {
            return false;
        } else if (request.returnValues().size() == 0) {
            return false;
        } else if (!request.checkReturnTypes("is")) {
            log.log(Level.WARNING, "Invalid return types for response: " + request.errorMessage());
            return false;
        }
        return true;
    }
Downloads file reference from config server and keeps track of files being downloaded

@author hmusum
filedistribution/src/main/java/com/yahoo/vespa/filedistribution/FileReferenceDownloader.java