storageImageSource.LayerInfosForCopy(): return uncompressed MediaTypes

Since #1138, we've been paying attention to the MediaType values
returned by LayerInfosForCopy(), so lying about layer data being
compressed when the data we provide isn't would cause uncompressed
layers to be mistakenly marked as compressed when we copied the image
without attempting to add or modify the compression of layers.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

storage/storage_image.go

@@ -246,8 +246,7 @@ func (s *storageImageSource) LayerInfosForCopy(ctx context.Context, instanceDige
 	case imgspecv1.MediaTypeImageManifest:
 		uncompressedLayerType = imgspecv1.MediaTypeImageLayer
 	case manifest.DockerV2Schema1MediaType, manifest.DockerV2Schema1SignedMediaType, manifest.DockerV2Schema2MediaType:
-		// This is actually a compressed type, but there's no uncompressed type defined
-		uncompressedLayerType = manifest.DockerV2Schema2LayerMediaType
+		uncompressedLayerType = manifest.DockerV2SchemaLayerMediaTypeUncompressed
 	}
 
 	physicalBlobInfos := []types.BlobInfo{}