Make the Kubelet read-only port configurable and disable it by default. Fixes #2159.

roles/kubernetes/node/templates/kubelet.kubeadm.env.j2

@@ -31,6 +31,7 @@ KUBELET_HOSTNAME="--hostname-override={{ kube_override_hostname }}"
 --cgroup-driver={{ kubelet_cgroup_driver|default(kubelet_cgroup_driver_detected) }} \
 --docker-disable-shared-pid={{ kubelet_disable_shared_pid }} \
 --anonymous-auth=false \
+--read-only-port={{ kube_read_only_port }} \
 {% if kube_version | version_compare('v1.8', '<') %}
 --experimental-fail-swap-on={{ kubelet_fail_swap_on|default(true)}} \
 {% else %}