add post render integration test (#576)

Signed-off-by: yxxhero <aiopsclub@163.com>

test/integration/test-cases/postrender-diff/input/add-cm1.bash

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+cat $1
+echo "---"
+
+cat <<EOS
+apiVersion: v1
+kind: ConfigMap
+data:
+  one: ONE
+metadata:
+  name: cm1
+EOS

test/integration/test-cases/postrender-diff/input/add-cm2.bash

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+cat $1
+echo "---"
+
+cat <<EOS
+apiVersion: v1
+kind: ConfigMap
+data:
+  two: TWO
+metadata:
+  name: cm2
+EOS

test/integration/test-cases/postrender-diff/input/helmfile.yaml

@@ -0,0 +1,39 @@
+helmDefaults:
+  postRenderer: ./add-cm1.bash
+
+releases:
+- name: foo
+  chart: ../../../charts/raw
+  values:
+  - templates:
+    - |
+      apiVersion: v1
+      kind: ConfigMap
+      metadata:
+        name: {{`{{ .Release.Name }}`}}-1
+        namespace: {{`{{ .Release.Namespace }}`}}
+      data:
+        foo: FOO
+    dep:
+      templates:
+      - |
+        apiVersion: v1
+        kind: ConfigMap
+        metadata:
+          name: {{`{{ .Release.Name }}`}}-2
+          namespace: {{`{{ .Release.Namespace }}`}}
+        data:
+          bar: BAR
+  postRenderer: ./add-cm2.bash
+- name: baz
+  chart: ../../../charts/raw
+  values:
+  - templates:
+    - |
+      apiVersion: v1
+      kind: ConfigMap
+      metadata:
+        name: {{`{{ .Release.Name }}`}}-3
+        namespace: {{`{{ .Release.Namespace }}`}}
+      data:
+        baz: BAZ