snapshot: add Close()

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

snapshot/overlay/overlay.go

@@ -401,3 +401,8 @@ func (o *snapshotter) upperPath(id string) string {
 func (o *snapshotter) workPath(id string) string {
 	return filepath.Join(o.root, "snapshots", id, "work")
 }
+
+// Close closes the snapshotter
+func (o *snapshotter) Close() error {
+	return o.ms.Close()
+}

snapshot/overlay/overlay_test.go

@@ -24,7 +24,7 @@ func newSnapshotter(ctx context.Context, root string) (snapshot.Snapshotter, fun
 		return nil, nil, err
 	}
 
-	return snapshotter, nil, nil
+	return snapshotter, func() error { return snapshotter.Close() }, nil
 }
 
 func TestOverlay(t *testing.T) {