update wordpress and mysql PV doc to use apps/v1beta2 APIs (#5424)

cn/docs/tutorials/stateful-application/mysql-wordpress-persistent-volume/mysql-deployment.yaml

@@ -25,13 +25,17 @@ spec:
     requests:
       storage: 20Gi
 ---
-apiVersion: extensions/v1beta1
+apiVersion: apps/v1beta2
 kind: Deployment
 metadata:
   name: wordpress-mysql
   labels:
     app: wordpress
 spec:
+  selector:
+    matchLabels:
+      app: wordpress
+      tier: mysql
   strategy:
     type: Recreate
   template:

cn/docs/tutorials/stateful-application/mysql-wordpress-persistent-volume/wordpress-deployment.yaml

@@ -25,13 +25,17 @@ spec:
     requests:
       storage: 20Gi
 ---
-apiVersion: extensions/v1beta1
+apiVersion: apps/v1beta2
 kind: Deployment
 metadata:
   name: wordpress
   labels:
     app: wordpress
 spec:
+  selector:
+    matchLabels:
+      app: wordpress
+      tier: frontend
   strategy:
     type: Recreate
   template:

docs/tutorials/stateful-application/mysql-wordpress-persistent-volume.md

@@ -151,7 +151,7 @@ The following manifest describes a single-instance WordPress Deployment and Serv
 
    You should see the WordPress set up page similar to the following screenshot.
 
-   ![wordpress-init](https://github.com/kubernetes/examples/blob/master/mysql-wordpress-pd/WordPress.png)
+   ![wordpress-init](https://raw.githubusercontent.com/kubernetes/examples/master/mysql-wordpress-pd/WordPress.png)
 
    **Warning:** Do not leave your WordPress installation on this page. If another user finds it, they can set up a website on your instance and use it to serve malicious content. <br/><br/>Either install WordPress by creating a username and password or delete your instance.
    {: .warning}

docs/tutorials/stateful-application/mysql-wordpress-persistent-volume/mysql-deployment.yaml

@@ -25,13 +25,17 @@ spec:
     requests:
       storage: 20Gi
 ---
-apiVersion: extensions/v1beta1
+apiVersion: apps/v1beta2
 kind: Deployment
 metadata:
   name: wordpress-mysql
   labels:
     app: wordpress
 spec:
+  selector:
+    matchLabels:
+      app: wordpress
+      tier: mysql
   strategy:
     type: Recreate
   template:

docs/tutorials/stateful-application/mysql-wordpress-persistent-volume/wordpress-deployment.yaml

@@ -25,13 +25,17 @@ spec:
     requests:
       storage: 20Gi
 ---
-apiVersion: extensions/v1beta1
+apiVersion: apps/v1beta2
 kind: Deployment
 metadata:
   name: wordpress
   labels:
     app: wordpress
 spec:
+  selector:
+    matchLabels:
+      app: wordpress
+      tier: frontend
   strategy:
     type: Recreate
   template: