private static Optional<Instant> lastModified(Path path) {
        try {
            return Optional.ofNullable(Files.getLastModifiedTime(path).toInstant());
        } catch (NoSuchFileException e) {
            return Optional.empty();
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }
Report Nginx metrics periodically.

@author Morten Tokle
@author Martin Polden
routing-generator/src/main/java/com/yahoo/vespa/hosted/routing/nginx/NginxMetricsReporter.java