Merge pull request #3297 from kolyshkin/1.0-3226

[1.0] Remove sub cgroup when container exits

libcontainer/cgroups/systemd/v2.go

@@ -5,7 +5,6 @@ package systemd
 import (
 	"fmt"
 	"math"
-	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -307,9 +306,10 @@ func (m *unifiedManager) Destroy() error {
 		return err
 	}
 
-	// XXX this is probably not needed, systemd should handle it
-	err := os.Remove(m.path)
-	if err != nil && !os.IsNotExist(err) {
+	// systemd 239 do not remove sub-cgroups.
+	err := cgroups.RemovePath(m.path)
+	// cgroups.RemovePath has handled ErrNotExist
+	if err != nil {
 		return err
 	}