Apply microk8s cgroups2 QOS patch (#550)

* Apply microk8s cgroups2 QOS patch

* Remove k8s patch and go instead with a docs patch

docs/src/snap/reference/troubleshooting.md

@@ -3,7 +3,8 @@
 This page provides techniques for troubleshooting common Canonical Kubernetes
 issues.
 
-## Kubectl error: "dial tcp 127.0.0.1:6443: connect: connection refused"
+
+## Kubectl error: `dial tcp 127.0.0.1:6443: connect: connection refused`
 
 ### Problem
 
@@ -33,6 +34,58 @@ Use `k8s config` instead of `k8s kubectl config` to generate a kubeconfig file
 that is valid for use on external machines.
 
 
+## Kubelet Error: `failed to initialize top level QOS containers`
+
+### Problem
+
+
+This is related to the `kubepods` cgroup not getting the cpuset controller up on
+the kubelet. kubelet needs a feature from cgroup and the kernel may not be set
+up appropriately to provide the cpuset feature.
+
+```
+E0125 00:20:56.003890    2172 kubelet.go:1466] "Failed to start ContainerManager" err="failed to initialize top level QOS containers: root container [kubepods] doesn't exist"
+```
+
+### Explanation
+
+An excellent deep-dive of the issue exists at 
+[kubernetes/kubernetes #122955][kubernetes-122955].
+
+Commenter [@haircommander][] [states][kubernetes-122955-2020403422]
+>  basically: we've figured out that this issue happens because libcontainer
+>  doesn't initialize the cpuset cgroup for the kubepods slice when the kubelet
+>  initially calls into it to do so. This happens because there isn't a cpuset
+>  defined on the top level of the cgroup. however, we fail to validate all of
+>  the cgroup controllers we need are present. It's possible this is a
+>  limitation in the dbus API: how do you ask systemd to create a cgroup that 
+>  is effectively empty?
+
+>  if we delegate: we are telling systemd to leave our cgroups alone, and not
+>  remove the "unneeded" cpuset cgroup.
+
+
+### Solution
+
+This is in the process of being fixed upstream via 
+[kubernetes/kuberetes #125923][kubernetes-125923].
+
+In the meantime, the best solution is to create a `Delegate=yes` configuration
+in systemd.
+
+```bash
+mkdir -p /etc/systemd/system/snap.k8s.kubelet.service.d
+cat /etc/systemd/system/snap.k8s.kubelet.service.d/delegate.conf <<EOF
+[Service]
+Delegate=yes
+EOF
+reboot
+```
+
 <!-- LINKS -->
 
 [kubeconfig file]: https://kubernetes.io/docs/concepts/configuration/organize-cluster-access-kubeconfig/
+[kubernetes-122955]: https://github.com/kubernetes/kubernetes/issues/122955
+[kubernetes-125923]: https://github.com/kubernetes/kubernetes/pull/125923
+[kubernetes-122955-2020403422]: https://github.com/kubernetes/kubernetes/issues/122955#issuecomment-2020403422
+[@haircommander]: https://github.com/haircommander