runc delete: call systemd's reset-failed

runc delete is supposed to remove all the container's artefacts.
In case systemd cgroup driver is used, and the systemd unit has failed
(e.g. oom-killed), systemd won't remove the unit (that is, unless the
"CollectMode: inactive-or-failed" property is set).

Call reset-failed from manager.Destroy so the failed unit will be
removed during "runc delete".

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/systemd/common.go

@@ -197,6 +197,10 @@ func stopUnit(cm *dbusConnManager, unitName string) error {
 			return errors.New("Timed out while waiting for systemd to remove " + unitName)
 		}
 	}
+
+	// In case of a failed unit, let systemd remove it.
+	_ = resetFailedUnit(cm, unitName)
+
 	return nil
 }