fix busybox image to 1.28 (issues with nslookup).

Changes where done with these commands:

reprec 'image: busybox(?!:)' 'image: busybox:1.28' */docs */examples
reprec -- '--image=busybox(?!:)' '--image=busybox:1.28' */docs */examples

Related issues:

 https://github.com/docker-library/busybox/issues/48
 https://github.com/kubernetes/kubernetes/issues/66924

content/en/examples/debug/counter-pod.yaml

@@ -5,6 +5,6 @@ metadata:
 spec:
   containers:
   - name: count
-    image: busybox
+    image: busybox:1.28
     args: [/bin/sh, -c,
             'i=0; while true; do echo "$i: $(date)"; i=$((i+1)); sleep 1; done']