Configure CoreDNS to shut down gracefully

This commit fixes bug 1884053.

https://bugzilla.redhat.com/show_bug.cgi?id=1884053

* assets/dns/daemonset.yaml: Specify a termination grace period of 120
seconds.  Change the readiness probe to use :8181/ready.
* pkg/manifests/bindata.go: Regenerate.
* pkg/operator/controller/controller_dns_configmap.go: (corefileTemplate):
Configure CoreDNS's health plugin to sleep 60 seconds when CoreDNS is shut
down.  Enable CoreDNS's ready plugin in order to provide a readiness
endpoint on :8181/ready, which stops responding when CoreDNS is shutting
down.
* pkg/operator/controller/controller_dns_configmap_test.go
(TestDesiredDNSConfigmap): Adjust for changes to corefileTemplate.
* pkg/operator/controller/controller_dns_daemonset.go
(daemonsetConfigChanged): Check if the readiness probe or termination grace
period changed, and update them if they did.
* pkg/operator/controller/controller_dns_daemonset_test.go
(TestDaemonsetConfigChanged): Add test cases to verify that
deploymentConfigChanged detects updates to
.spec.template.spec.containers[].readinessProbe.httpGet and
.spec.template.spec.terminationGracePeriodSeconds.

assets/dns/daemonset.yaml

@@ -26,8 +26,8 @@ spec:
           protocol: TCP
         readinessProbe:
           httpGet:
-            path: /health
-            port: 8080
+            path: /ready
+            port: 8181
             scheme: HTTP
           initialDelaySeconds: 10
           periodSeconds: 10
@@ -152,6 +152,7 @@ spec:
       dnsPolicy: Default
       nodeSelector:
         kubernetes.io/os: linux      
+      terminationGracePeriodSeconds: 120
       volumes:
       - name: config-volume
         configMap:

pkg/operator/controller/controller_dns_configmap.go

@@ -31,7 +31,10 @@ var corefileTemplate = template.Must(template.New("Corefile").Parse(`{{range .Se
 {{end -}}
 .:5353 {
     errors
-    health
+    health {
+        lameduck 60s
+    }
+    ready
     kubernetes {{.ClusterDomain}} in-addr.arpa ip6.arpa {
         pods insecure
         upstream

pkg/operator/controller/controller_dns_configmap_test.go

@@ -43,7 +43,10 @@ bar.com:5353 example.com:5353 {
 }
 .:5353 {
     errors
-    health
+    health {
+        lameduck 60s
+    }
+    ready
     kubernetes cluster.local in-addr.arpa ip6.arpa {
         pods insecure
         upstream