Upgrade kubernetes to v1.12.0 (#3410)

* Upgrade kubernetes to v1.12.0

Use kubeadm v1alpha3 config

* Upgrade coredns and etcd

* Upgrage docker to 18.06

roles/kubespray-defaults/defaults/main.yaml

@@ -16,7 +16,7 @@ is_atomic: false
 disable_swap: true
 
 ## Change this to use another Kubernetes version, e.g. a current beta release
-kube_version: v1.11.3
+kube_version: v1.12.0
 
 ## Kube Proxy mode One of ['iptables','ipvs']
 kube_proxy_mode: iptables
@@ -276,13 +276,24 @@ kubelet_authentication_token_webhook: true
 # When enabled, access to the kubelet API requires authorization by delegation to the API server
 kubelet_authorization_mode_webhook: false
 
-## List of key=value pairs that describe feature gates for
-## the k8s cluster.
-kube_feature_gates:
+## v1.11 feature
+feature_gate_v1_11:
   - "PersistentLocalVolumes={{ local_volume_provisioner_enabled | string }}"
   - "VolumeScheduling={{ local_volume_provisioner_enabled | string }}"
   - "MountPropagation={{ local_volume_provisioner_enabled | string }}"
 
+## v1.12 feature
+feature_gate_v1_12: []
+
+## List of key=value pairs that describe feature gates for
+## the k8s cluster.
+kube_feature_gates: |-
+  {%- if kube_version | version_compare('v1.12.0', '<') -%}
+  {{ feature_gate_v1_11 }}
+  {%- else -%}
+  {{ feature_gate_v1_12 }}
+  {%- endif %}
+
 # Vault data dirs.
 vault_base_dir: /etc/vault
 vault_cert_dir: "{{ vault_base_dir }}/ssl"