In the recent PR on adding ProcMount, we introduced a regression when
pods are privileged. This shows up in 18.06 docker with kubeadm in the
kube-proxy container.

The kube-proxy container is privilged, but we end up setting the
`/proc/sys` to Read-Only which causes failures when running kube-proxy
as a pod. This shows up as a failure when using sysctl to set various
network things.

Change-Id: Ic61c4c9c961843a4e064e783fab0b54350762a8d