Switch language name 'zh' to 'zh-cn'

This is the first step to rename 'zh' to 'zh-cn'. There are several reasons why we rename the language name.

- The upstream docsy theme changed the language name, leading to many warnings during site build;
  The side-effect is that the i18n strings are no longer working.
- We believe renaming the language is the right thing to do, because this move can make room for other variants of Chinese language, such as 'zh-tw', 'zh-sg' etc.

There would be several follow-ups to this PR, such as fixing the intra-site links, adding redirects etc.

We will lock up changes to zh/zh-cn pages for the moment, until this one gets in.

This PR is based on commit cdad0a7342.

content/zh-cn/examples/application/wordpress/mysql-deployment.yaml

@@ -0,0 +1,65 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: wordpress-mysql
+  labels:
+    app: wordpress
+spec:
+  ports:
+    - port: 3306
+  selector:
+    app: wordpress
+    tier: mysql
+  clusterIP: None
+---
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: mysql-pv-claim
+  labels:
+    app: wordpress
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 20Gi
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: wordpress-mysql
+  labels:
+    app: wordpress
+spec:
+  selector:
+    matchLabels:
+      app: wordpress
+      tier: mysql
+  strategy:
+    type: Recreate
+  template:
+    metadata:
+      labels:
+        app: wordpress
+        tier: mysql
+    spec:
+      containers:
+      - image: mysql:5.6
+        name: mysql
+        env:
+        - name: MYSQL_ROOT_PASSWORD
+          valueFrom:
+            secretKeyRef:
+              name: mysql-pass
+              key: password
+        ports:
+        - containerPort: 3306
+          name: mysql
+        volumeMounts:
+        - name: mysql-persistent-storage
+          mountPath: /var/lib/mysql
+      volumes:
+      - name: mysql-persistent-storage
+        persistentVolumeClaim:
+          claimName: mysql-pv-claim

content/zh-cn/examples/application/wordpress/wordpress-deployment.yaml

@@ -0,0 +1,67 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: wordpress
+  labels:
+    app: wordpress
+spec:
+  ports:
+    - port: 80
+  selector:
+    app: wordpress
+    tier: frontend
+  type: LoadBalancer
+---
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: wp-pv-claim
+  labels:
+    app: wordpress
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 20Gi
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: wordpress
+  labels:
+    app: wordpress
+spec:
+  selector:
+    matchLabels:
+      app: wordpress
+      tier: frontend
+  strategy:
+    type: Recreate
+  template:
+    metadata:
+      labels:
+        app: wordpress
+        tier: frontend
+    spec:
+      containers:
+      - image: wordpress:4.8-apache
+        name: wordpress
+        env:
+        - name: WORDPRESS_DB_HOST
+          value: wordpress-mysql
+        - name: WORDPRESS_DB_PASSWORD
+          valueFrom:
+            secretKeyRef:
+              name: mysql-pass
+              key: password
+        ports:
+        - containerPort: 80
+          name: wordpress
+        volumeMounts:
+        - name: wordpress-persistent-storage
+          mountPath: /var/www/html
+      volumes:
+      - name: wordpress-persistent-storage
+        persistentVolumeClaim:
+          claimName: wp-pv-claim