skip already exists content

Signed-off-by: Evan Hazlett <ejhazlett@gmail.com>

container.go

@@ -325,9 +325,12 @@ func (c *container) Checkpoint(ctx context.Context, ref string, opts ...Checkpoi
 	// process remaining opts
 	for _, o := range opts {
 		if err := o(ctx, c.client, &info, index, copts); err != nil {
+			err = errdefs.FromGRPC(err)
+			if !errdefs.IsAlreadyExists(err) {
 				return nil, err
 			}
 		}
+	}
 
 	desc, err := writeIndex(ctx, index, c.client, c.ID()+"index")
 	if err != nil {