private boolean olderThan(LogFile lf, long days, long now) {
        long mtime = lf.path.lastModified();
        long diff = now - mtime;
        return (diff > days * 86400L * 1000L);
    }
Creates an instance of FilesArchive managing the given directory
logserver/src/main/java/com/yahoo/logserver/handlers/archive/FilesArchived.java