void completedDownloading(FileReference fileReference, File file) {
        Optional<FileReferenceDownload> download = get(fileReference);
        setDownloadStatus(fileReference, 1.0);
        if (download.isPresent()) {
            downloads.remove(fileReference);
            download.get().future().complete(Optional.of(file));
        } else {
            log.log(Level.FINE, () -> "Received '" + fileReference + "', which was not requested. Can be ignored if happening during upgrades/restarts");
        }
    }
Keeps track of downloads and download status

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