message: nydus-image: fix ut of node
  UT needs to be updated after Node honors "version".
diff: @@ -1671,7 +1671,7 @@ mod tests {
  let pa = TempDir::new().unwrap();
  let pa_aa = TempFile::new_in(pa.as_path()).unwrap();
  let mut node = Node::new(
  - RafsVersion::V5,
  + RafsVersion::V6,
  pa.as_path().to_path_buf(),
  pa_aa.as_path().to_path_buf(),
  Overlay::UpperAddition,
  @@ -1706,7 +1706,7 @@ mod tests {
  fs::symlink(pa_aa.as_path(), &pa_sym).unwrap();
  let mut sym_node = Node::new(
  - RafsVersion::V5,
  + RafsVersion::V6,
  pa.as_path().to_path_buf(),
  pa_sym.as_path().to_path_buf(),
  Overlay::UpperAddition,
  @@ -1731,7 +1731,7 @@ mod tests {
  );
  let mut dir_node = Node::new(
  - RafsVersion::V5,
  + RafsVersion::V6,
  pa.as_path().to_path_buf(),
  pa.as_path().to_path_buf(),
  Overlay::UpperAddition,
  