assert that number of pods on node does not exceed CIDR address range

The number of pods on a given node is determined by the  --max-pods=k
directive. When the address space is exhausted, no more pods can be
scheduled even if from the --max-pods-perspective, the node still has
capacity.

The special case that a pod is scheduled and uses the node IP in the
host network namespace is too "soft" to derive a guarantee.

Comparing kubelet_max_pods with kube_network_node_prefix when given
allows to assert that pod limits match the CIDR address space.

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

@@ -28,6 +28,7 @@ KUBELET_HOSTNAME="--hostname-override={{ kube_override_hostname }}"
 {% endif %}
 --cgroup-driver={{ kubelet_cgroup_driver|default(kubelet_cgroup_driver_detected) }} \
 --cgroups-per-qos={{ kubelet_cgroups_per_qos }} \
+--max-pods={{ kubelet_max_pods }} \
 {% if kube_version | version_compare('v1.8', '<') %}
 --experimental-fail-swap-on={{ kubelet_fail_swap_on|default(true)}} \
 {% else %}