test for explicit null value propagation in apply

hack/testdata/null-propagation/deployment-l1.yaml

@@ -0,0 +1,13 @@
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: my-depl
+spec:
+  template:
+    metadata:
+      labels:
+        l1: l1
+    spec:
+      containers:
+      - name: nginx
+        image: gcr.io/google-containers/nginx:1.7.9

hack/testdata/null-propagation/deployment-l2.yaml

@@ -0,0 +1,17 @@
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: my-depl
+  # We expect this field to be defaulted to the new label l2
+  labels: null
+spec:
+  # We expect this field to be defaulted to the new label l2
+  selector: null
+  template:
+    metadata:
+      labels:
+        l2: l2
+    spec:
+      containers:
+      - name: nginx
+        image: gcr.io/google-containers/nginx:1.7.9