Add snapshot walk implementations

Temporarily remove zfs and aufs until interface update

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

snapshots/windows/windows.go

@@ -238,14 +238,14 @@ func (s *snapshotter) Remove(ctx context.Context, key string) error {
 }
 
 // Walk the committed snapshots.
-func (s *snapshotter) Walk(ctx context.Context, fn func(context.Context, snapshots.Info) error, filters ...string) error {
+func (s *snapshotter) Walk(ctx context.Context, fn snapshots.WalkFunc, fs ...string) error {
 	ctx, t, err := s.ms.TransactionContext(ctx, false)
 	if err != nil {
 		return err
 	}
 	defer t.Rollback()
 
-	return storage.WalkInfo(ctx, fn)
+	return storage.WalkInfo(ctx, fn, fs...)
 }
 
 // Close closes the snapshotter