fixes RBAC permissions for task and pipeline runs for openshift

When `taskruns` or  `pipelineruns` instance is created, build pod creation
fails with following error `tekton-pipelines-controller` service account.

```
'pods "hello-task-64f24-r9sgt" is forbidden: cannot set blockOwnerDeletion
if an ownerReference refers to a resource you can't set finalizers on: no RBAC
policy matched, <nil>'
```

This patch fixes the required permission for `tekton-pipelines-admin` role,
so controller could set required metadata on build pod.

Fixes
 - knative/build#523

config/200-clusterrole.yaml

@@ -18,6 +18,9 @@ rules:
  - apiGroups: ["tekton.dev"]
  resources: ["tasks", "clustertasks", "taskruns", "pipelines", "pipelineruns", "pipelineresources"]
  verbs: ["get", "list", "create", "update", "delete", "patch", "watch"]
+ - apiGroups: ["tekton.dev"]
+ resources: ["taskruns/finalizers", "pipelineruns/finalizers"]
+ verbs: ["get", "list", "create", "update", "delete", "patch", "watch"]
  - apiGroups: ["tekton.dev"]
  resources: ["tasks/status", "clustertasks/status", "taskruns/status", "pipelines/status", "pipelineruns/status", "pipelineresources/status"]
  verbs: ["get", "list", "create", "update", "delete", "patch", "watch"]