Merge branch 'master' of https://github.com/kubernetes-incubator/kubespray into cert-fix-2

docs/vars.md

roles/kubernetes-apps/ansible/tasks/main.yml

...ngress_nginx/templates/ingress-nginx-controller-ds.yml.j2

roles/kubernetes/master/tasks/pre-upgrade.yml

roles/kubernetes/master/templates/kubeadm-config.yaml.j2

roles/kubernetes/node/tasks/main.yml

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

...ubernetes/node/templates/manifests/kube-proxy.manifest.j2

roles/kubernetes/preinstall/tasks/main.yml

tests/ansible.cfg