The reason for this PR is that in most cases
we utilize systemd cgroup driver nowadays.
So it worth it to set kubepods.slice cgroup root
by default.
https: //github.com/kubernetes/kubernetes/blob/release-1.26/pkg/kubelet/cm/cgroup_manager_linux.go#L77-L81
Change-Id: I0cad148eb827439815c7e5bad1d6b6108cd1ab8d