vendor containerd/cgroups

We need to vendor in the latest containerd/cgroups for a fix related to
slice delegation and systemd <= 239. The opencontainer/runtime-spec is
brought along for the ride.

Signed-off-by: baude <bbaude@redhat.com>

Closes: #1414
Approved by: mheon

vendor/github.com/containerd/cgroups/control.go

@@ -1,3 +1,19 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
 package cgroups
 
 import (
@@ -8,6 +24,7 @@ import (
 
 const (
 	cgroupProcs    = "cgroup.procs"
+	cgroupTasks    = "tasks"
 	defaultDirPerm = 0755
 )
 
@@ -32,8 +49,10 @@ type Process struct {
 type Cgroup interface {
 	// New creates a new cgroup under the calling cgroup
 	New(string, *specs.LinuxResources) (Cgroup, error)
-	// Add adds a process to the cgroup
+	// Add adds a process to the cgroup (cgroup.procs)
 	Add(Process) error
+	// AddTask adds a process to the cgroup (tasks)
+	AddTask(Process) error
 	// Delete removes the cgroup as a whole
 	Delete() error
 	// MoveTo moves all the processes under the calling cgroup to the provided one