RFE: enhance nydus-image/nydusify check to do full filesystem check

[eryugey]

Currently "nydus-image check" sub-command only checks if the converted image is in valid rafs format, and doesn't do full filesystem integrity check.

We'd better to enhance nydus-image check to do full filesystem integrity check without mounting rafs.

[imeoer]

1. nydusify check need to check dev, rdev, symlink, project id, uid, gid, nlink, ctime between source image and nydus image.
2. currently nydusify check only checks filesystem data (chunks) if the user provides --backend-type registry and --backend-config ..., we need to remove this limitation (e.g. automatically read registry auth from docker config).
3. currently nydusify check requires docker to be installed (for pulling source image and mounting all layers by overlayfs), we need to remove this limitation, and pull, unpack and mount image layer by nydusify self.
4. nydusify check provides --source-type directory or --source-type tar option to support code package filesystem consistency check.

[adamqqqplay]

Finished in #543