'kubeadm reset' uses incorrect way of unmounting /var/lib/kubelet
directories. It queries /proc/mounts for /var/lib/kubelet mount point.
If /var/lib/kubelet directory is also mounted it makes 'kubelet reset'
to unmount it too, which is incorrect. It also makes it fail as it
can't unmount /var/lib/kubelet before unmounting mounts inside it.
Fixed by querying /var/lib/kubelet/ instead of /var/lib/kubelet.
This should exclude /var/lib/kubelet from the query results even if
it's mounted.
Fixes: kubernetes/kubeadm#1294
48a961cfa2