add a simple curl source service sample

demos/apps/sleep/README.md

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+# Simple sleep service
+
+This sample consists of a simple service that does nothing but sleep. 
+It's a ubuntu container with curl installed that can be used as a request source for invoking other services
+to experiment with Istio networking.
+To use it:
+
+1. Install Istio by following the [istio install instructions](https://istio.io/docs/tasks/installing-istio.html).
+
+2. Start the sleep service:
+
+   ```bash
+   kubectl apply -f <(istioctl kube-inject -f sleep.yaml)
+   ```
+
+   Note that if you also want to be able to directly call
+   external services, you'll need to set the `--includeIPRanges` option of `kube-inject`.
+   See [configuring egress](https://istio.io/docs/tasks/egress.html) for details.
+
+3. Start some other services, for example, the [Bookinfo sample](https://istio.io/docs/samples/bookinfo.html).
+
+Now you can `kubectl exec` into the sleep service to experiment with Istio.
+For example, the following commands can be used curl to call the Bookinfo `ratings` service:
+
+```bash
+$ export SLEEP_POD=$(kubectl describe pod sleep- | awk '$1 == "Name:"{print $2}')
+$ kubectl exec -it $SLEEP_POD -c sleep bash
+root@sleep-342146846-kbj55:/# curl http://ratings.default.svc.cluster.local:9080/ratings
+{"Reviewer1":5,"Reviewer2":4}
+root@sleep-342146846-kbj55:/#
+```

demos/apps/sleep/sleep.yaml

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+apiVersion: v1
+kind: Service
+metadata:
+  name: sleep
+  labels:
+    app: sleep
+spec:
+  ports:
+  - port: 80
+    name: http
+  selector:
+    app: sleep
+---
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: sleep
+spec:
+  replicas: 1
+  template:
+    metadata:
+      labels:
+        app: sleep
+    spec:
+      containers:
+      - name: sleep
+        image: tutum/curl
+        command: ["/bin/sleep","infinity"]
+        imagePullPolicy: IfNotPresent
+        ports:
+        - containerPort: 80
+---