Add flags for prometheus-to-sd components.

Configure prometheus-to-sd-endpoint and prometheus-to-sd-prefix base on
the environment.

cluster/addons/cluster-monitoring/stackdriver/heapster-controller.yaml

@@ -63,12 +63,14 @@ spec:
             - name: usr-ca-certs
               mountPath: /usr/share/ca-certificates
               readOnly: true
+        # BEGIN_PROMETHEUS_TO_SD
         - name: prom-to-sd
           image: gcr.io/google-containers/prometheus-to-sd:v0.2.1
           command:
             - /monitor
             - --source=heapster:http://localhost:8082?whitelisted=stackdriver_requests_count,stackdriver_timeseries_count
-            - --stackdriver-prefix=container.googleapis.com/internal/addons
+            - --stackdriver-prefix={{ prometheus_to_sd_prefix }}/addons
+            - --api-override={{ prometheus_to_sd_endpoint }}
             - --pod-id=$(POD_NAME)
             - --namespace-id=$(POD_NAMESPACE)
           volumeMounts:
@@ -83,6 +85,7 @@ spec:
               valueFrom:
                 fieldRef:
                   fieldPath: metadata.namespace
+        # END_PROMETHEUS_TO_SD
         - image: gcr.io/google_containers/addon-resizer:2.0
           name: heapster-nanny
           resources: