fix: allow non-OCI layers

opencontainers/image-spec#1190
https://www.cyphar.com/blog/post/20190121-ociv2-images-i-tar

As part of improving handling large images and also broadly considering
building layers as full mountable filesystems, relax the layer type
check.

This allows containerd clients to pull and produce rootfs simply by
mounting them.

Signed-off-by: Ramkumar Chinchani <[email protected]>

Author: rchincha

client/image.go

@@ -391,9 +391,7 @@ func (i *image) getLayers(ctx context.Context, manifest ocispec.Manifest) ([]roo
 	// parse out the image layers from oci artifact layers
 	imageLayers := []ocispec.Descriptor{}
 	for _, ociLayer := range manifest.Layers {
-		if images.IsLayerType(ociLayer.MediaType) {
-			imageLayers = append(imageLayers, ociLayer)
-		}
+		imageLayers = append(imageLayers, ociLayer)
 	}
 	if len(diffIDs) != len(imageLayers) {
 		return nil, errors.New("mismatched image rootfs and manifest layers")