allow kubectl subcmds to process multiple resources

- use resource.Visit() to recursively process resources, as well as, aggregate
errors where possible

hack/testdata/recursive/pod-modify/busybox.yaml

@@ -0,0 +1,16 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: busybox0
+  labels:
+    app: busybox0
+    status: replaced
+spec:
+  containers:
+  - image: busybox
+    command:
+      - sleep
+      - "3600"
+    imagePullPolicy: IfNotPresent
+    name: busybox
+  restartPolicy: Always

hack/testdata/recursive/pod-modify/pod/busybox-broken.yaml

@@ -0,0 +1,16 @@
+apiVersion: v1
+ind: Pod
+metadata:
+  name: busybox2
+  labels:
+    app: busybox2
+    status: replaced
+spec:
+  containers:
+  - image: busybox
+    command:
+      - sleep
+      - "3600"
+    imagePullPolicy: IfNotPresent
+    name: busybox
+  restartPolicy: Always

hack/testdata/recursive/pod-modify/pod/busybox.yaml

@@ -0,0 +1,16 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: busybox1
+  labels:
+    app: busybox1
+    status: replaced
+spec:
+  containers:
+  - image: busybox
+    command:
+      - sleep
+      - "3600"
+    imagePullPolicy: IfNotPresent
+    name: busybox
+  restartPolicy: Always