Install Kubernetes 1.11 and go back to Ubuntu Xenial until Bionic is officially supported

roles/kubernetes/templates/kubeadm-config.j2

@@ -0,0 +1,27 @@
+apiVersion: kubeadm.k8s.io/v1alpha2
+kind: MasterConfiguration
+api:
+  advertiseAddress: {{ api_floating_ip if groups.k8s_masters | length > 1 else hostvars[initial_master].vpn_ip }}
+etcd:
+  external:
+    endpoints:
+{% for host in groups['k8s_masters'] %}
+    - "http://{{ hostvars[host]['vpn_ip'] }}:2379"
+{% endfor %}
+networking:
+  podSubnet: "{{ pod_subnet }}"
+kubernetesVersion: "{{ kubernetes_version }}"
+apiServerCertSANs:
+{% for host in groups['k8s_masters'] %}
+- "{{ hostvars[host]['vpn_ip'] }}"
+{% endfor %}
+- "{{ api_floating_ip }}"
+- "127.0.0.1"
+bootstrapTokens:
+- groups:
+  - system:bootstrappers:kubeadm:default-node-token
+  token: "{{ hostvars[initial_master].kubeadm_token }}"
+  ttl: 0s
+  usages:
+  - signing
+  - authentication