Update RBAC permissions in examples/k8s

[fbarl]

While trying to test #3589 in a local Minikube instance following the instructions from https://www.weave.works/docs/scope/latest/installing/#kubernetes-local-clone, I figured almost all K8s node details actions were being rejected based on the RBAC permission setting:

• "services "weave-scope-app" is forbidden: User "system:serviceaccount:weave:weave-scope" cannot get resource "services" in API group "" in the namespace "weave""
• "deployments.extensions "weave-scope-cluster-agent" is forbidden: User "system:serviceaccount:weave:weave-scope" cannot get resource "deployments/scale" in API group "extensions" in the namespace "weave""
• "deployments.apps "weave-scope-cluster-agent" is forbidden: User "system:serviceaccount:weave:weave-scope" cannot get resource "deployments" in API group "apps" in the namespace "weave""
• "pods "weave-scope-cluster-agent-84df69896b-dv5zf" is forbidden: User "system:serviceaccount:weave:weave-scope" cannot get resource "pods/log" in API group "" in the namespace "weave""
• "pods "weave-scope-agent-jc4vk" is forbidden: User "system:serviceaccount:weave:weave-scope" cannot delete resource "pods" in API group "" in the namespace "weave""
• "pods "weave-scope-agent-jc4vk" is forbidden: User "system:serviceaccount:weave:weave-scope" cannot get resource "pods" in API group "" in the namespace "weave""

To fix this, we should add all of these to cluster-role.yaml.