Improve check for cgroup2 availability (#3413)

The cgroup2 mount may sometimes appear as:

```
$ mount -t cgroup2
none on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime)
```

Author: neoaggelos

microk8s-resources/wrappers/run-containerd-with-args

@@ -53,7 +53,7 @@ RUNTIME="runc"
 RUNTIME_TYPE="io.containerd.runc.v1"
 SNAPSHOTTER=$(snapshotter)
 
-if mount | grep -q 'cgroup2 on /sys/fs/cgroup'; then
+if mount -t cgroup2 | grep -q 'type cgroup2'; then
   RUNTIME_TYPE="io.containerd.runc.v2"
 fi