snapshot: add Close()

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

snapshot/btrfs/btrfs.go

@@ -370,3 +370,8 @@ func (b *snapshotter) Remove(ctx context.Context, key string) (err error) {
 
 	return nil
 }
+
+// Close closes the snapshotter
+func (b *snapshotter) Close() error {
+	return b.ms.Close()
+}

snapshot/btrfs/btrfs_test.go

@@ -47,6 +47,9 @@ func boltSnapshotter(t *testing.T) func(context.Context, string) (snapshot.Snaps
 		}
 
 		return snapshotter, func() error {
+			if err := snapshotter.Close(); err != nil {
+				return err
+			}
 			err := mount.UnmountAll(root, unix.MNT_DETACH)
 			if cerr := cleanupDevice(); cerr != nil {
 				err = errors.Wrap(cerr, "device cleanup failed")