Return image references in ImageStatus()

The image's canonical reference is a name with a digest of the image's
manifest, so compute and return that value as the image's reference in
ImageStatus() and in ContainerStatus().

We don't auto-store a name based on the image digest when we pull one by
tag, but then CRI doesn't need us to do that.

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

server/image_status.go

@@ -42,10 +42,10 @@ func (s *Server) ImageStatus(ctx context.Context, req *pb.ImageStatusRequest) (*
 	}
 	resp := &pb.ImageStatusResponse{
 		Image: &pb.Image{
-			Id:       status.ID,
-			RepoTags: status.Names,
-			Size_:    *status.Size,
-			// TODO: https://github.com/kubernetes-incubator/cri-o/issues/531
+			Id:          status.ID,
+			RepoTags:    status.Names,
+			RepoDigests: status.Digests,
+			Size_:       *status.Size,
 		},
 	}
 	logrus.Debugf("ImageStatusResponse: %+v", resp)