private static Stream<Path> walk(Path path) {
        try {
            return Files.walk(path);
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }
Returns List of all def-files in all defFilesDirectories, including path.
@return The list of def-files.
config-class-plugin/src/main/java/com/yahoo/vespa/ConfigGenMojo.java