Replace references to Replication Controllers with Deployments in docs/user-guide/walkthrough.

Also:
* Cleanup pasted yaml and instead embed file
* Clarify Service test sections by including busybox exec commands as part of the preformatted section

docs/user-guide/walkthrough/deployment.yaml

@@ -0,0 +1,18 @@
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: nginx-deployment
+spec:
+  replicas: 2 # tells deployment to run 2 pods matching the template
+  template: # create pods using pod definition in this template
+    metadata:
+      # unlike pod-nginx.yaml, the name is not included in the meta data as a unique name is
+      # generated from the deployment name
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.7.9
+        ports:
+        - containerPort: 80