enable imageTagTransformer in application

Author: Liujingfang1

pkg/app/application.go

@@ -168,11 +168,20 @@ func (a *Application) loadCustomizedResMap() (resmap.ResMap, error) {
 	if len(errs.Get()) > 0 {
 		return nil, errs
 	}
+
+	var r []transformers.Transformer
 	t, err := a.newTransformer(patches)
 	if err != nil {
 		return nil, err
 	}
-	err = t.Transform(result)
+	r = append(r, t)
+	t, err = transformers.NewImageTagTransformer(a.kustomization.ImageTags)
+	if err != nil {
+		return nil, err
+	}
+	r = append(r, t)
+
+	err = transformers.NewMultiTransformer(r).Transform(result)
 	if err != nil {
 		return nil, err
 	}

pkg/commands/testdata/testcase-simple/expected.diff

@@ -48,7 +48,7 @@ diff -u -N /tmp/noop/extensions_v1beta1_Deployment_mungebot.yaml /tmp/transforme
          - name: foo
            value: bar
 -        image: nginx
-+        image: nginx:1.7.9
++        image: nginx:1.8.0
          name: nginx
          ports:
          - containerPort: 80

pkg/commands/testdata/testcase-simple/expected.yaml

@@ -111,7 +111,7 @@ spec:
               name: test-infra-app-tls-6hkmhf2224
         - name: foo
           value: bar
-        image: nginx:1.7.9
+        image: nginx:1.8.0
         name: nginx
         ports:
         - containerPort: 80

pkg/examplelayout/simple/instances/exampleinstance/kustomization.yaml

@@ -21,3 +21,6 @@ secretGenerator:
     tls.crt: "cat secret/tls.cert"
     tls.key: "cat secret/tls.key"
   type: "kubernetes.io/tls"
+imageTags:
+- name: nginx
+  newTag: 1.8.0