Use image constructor in client

Replace manual image struct creation with the image
constructor which is there to do just that.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

task.go

@@ -458,10 +458,7 @@ func (t *task) Checkpoint(ctx context.Context, opts ...CheckpointTaskOpts) (Imag
 	if im, err = t.client.ImageService().Create(ctx, im); err != nil {
 		return nil, err
 	}
-	return &image{
-		client: t.client,
-		i:      im,
-	}, nil
+	return NewImage(t.client, im), nil
 }
 
 // UpdateTaskInfo allows updated specific settings to be changed on a task