message: rafs: no need to new a io error
  Rafs just use error code wrapper to last unexpected error up.
  We just log a error line here.
diff: @@ -85,10 +85,12 @@ impl dyn RafsIoRead {
  }
  pub fn from_file(path: &str) -> RafsResult<Box<dyn RafsIoRead>> {
  - Ok(Box::new(File::open(path).map_err(|err| {
  - last_error!(format!("Failed to open file {:?}: {:?}", path, err));
  - RafsError::ReadMetadata(err)
  - })?))
  + let f = File::open(path).map_err(|e| {
  + error!("Failed to open rafs meta file {:?}: {:?}", path, e);
  + RafsError::ReadMetadata(e)
  + })?;
  +
  + Ok(Box::new(f))
  }
  }
  