examples/nginx/rbac: Give access to own namespace

[chancez]

Even with --force-namespace-isolation, nginx-ingress-controller still queries for it's own namespace, so give it access to querying namespaces within it's namespace in the nginx-ingress-role.

[k8s-reviewable]

This change is 

[coveralls]

Coverage remained the same at 43.925% when pulling 8cd18bc on chancez:patch-2 into fbb96f4 on kubernetes:master.

[aledbf]

/lgtm

[aledbf]

@chancez thanks!

[redbaron]

I dont think it achieves desired effect, Namespace is not a namespaced resource, therefore it outside of control of Role, it must be ClusterRole.

For those who stumble upon it, here is solution which works:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: ingress-prod
  annotations:
rules:
  - apiGroups:
      - ""
    resources:
      - namespaces
    resourceNames:
      - prod
    verbs:
      - get

key is to use resourceNames.