Fixes in Test KFServing installation documentation (kubeflow#838)

* Avoid using namespace with control panel label
Use a dedicated namespace for inferenceservice test

* Kubectl command to Fetch hostname to be used in the header curl
Since hostname consists namespace (sklearn-iris.default.example.com)
it might be misleading to document it explicitly since users might
use other namespaces than default

@chipchaderez

README.md

@@ -79,18 +79,20 @@ Please refer to our [troubleshooting section](docs/DEVELOPER_GUIDE.md#troublesho
 2) Wait all pods to be ready then launch KFServing `InferenceService`.(wait 1 min for everything to be ready and 40s to
 launch the `InferenceService`)
 ```bash
-kubectl apply -f docs/samples/sklearn/sklearn.yaml
+kubectl create namespace kfserving-test
+kubectl apply -f docs/samples/sklearn/sklearn.yaml -n kfserving-test
 ```
 3) Check KFServing `InferenceService` status.
 ```bash
-kubectl get inferenceservices sklearn-iris
+kubectl get inferenceservices sklearn-iris -n kfserving-test
 NAME           URL                                                              READY   DEFAULT TRAFFIC   CANARY TRAFFIC   AGE
-sklearn-iris   http://sklearn-iris.default.example.com/v1/models/sklearn-iris   True    100                                109s
+sklearn-iris   http://sklearn-iris.kfserving-test.example.com/v1/models/sklearn-iris   True    100                                109s
 ```
 4) Curl the `InferenceService`
 ```bash
 kubectl port-forward --namespace istio-system $(kubectl get pod --namespace istio-system --selector="app=istio-ingressgateway" --output jsonpath='{.items[0].metadata.name}') 8080:80
-curl -v -H "Host: sklearn-iris.default.example.com" http://localhost:8080/v1/models/sklearn-iris:predict -d @./docs/samples/sklearn/iris-input.json
+SERVICE_HOSTNAME=$(kubectl get inferenceservice sklearn-iris -n kfserving-test -o jsonpath='{.status.url}' | cut -d "/" -f 3)
+curl -v -H "Host: ${SERVICE_HOSTNAME}" http://localhost:8080/v1/models/sklearn-iris:predict -d @./docs/samples/sklearn/iris-input.json
 ```
 ### Use KFServing SDK
 * Install the SDK