[RBAC] Add role binging for prometheus-server

In case of using RBAC in k8s we need to create role binding for
prometheus-server user to unlock creation of kubernetes-api target in
prometheus, otherwise we will get error:
`User \"prometheus-server\" cannot list nodes at the cluster scope`

Change-Id: I7ec27483f16169a5040aad24c9076c6361e02127
diff --git a/tests/pillar/pool_cluster_with_domain.sls b/tests/pillar/pool_cluster_with_domain.sls
index 595e39e..f756dd4 100644
--- a/tests/pillar/pool_cluster_with_domain.sls
+++ b/tests/pillar/pool_cluster_with_domain.sls
@@ -22,6 +22,8 @@
         hosts:
         - cmp01
         - cmp02
+    monitoring:
+      backend: prometheus
   pool:
     enabled: true
     version: v1.2.0