Add ready plugin for CoreDNS (#4817)

roles/kubernetes-apps/ansible/templates/coredns-config.yml.j2

@@ -11,6 +11,7 @@ data:
     .:53 {
         errors
         health
+        ready
         kubernetes {{ dns_domain }} in-addr.arpa ip6.arpa {
           pods insecure
 {% if resolvconf_mode == 'host_resolvconf' and upstream_dns_servers is defined and upstream_dns_servers|length > 0 %}

roles/kubernetes-apps/ansible/templates/coredns-deployment.yml.j2

@@ -96,8 +96,8 @@ spec:
           failureThreshold: 10
         readinessProbe:
           httpGet:
-            path: /health
-            port: 8080
+            path: /ready
+            port: 8181
             scheme: HTTP
           timeoutSeconds: 5
           successThreshold: 1