Issue description

The kubernetes package should be upgraded from 1.10 to 1.11.

With this upgrade will also follow some refactorings of the nixos kubernetes module, because of the many kubenetes API-changes. See: https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.11.md

Changes to module nixos/kubernetes could include:

• Implement use of kubelet auto TLS-bootstrapping: https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/, https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/

• Removal of access to insecure ports in the cluster

• Replace KubeDNS with CoreDNS