allow hostpath provisioner to delete persistent volumes when RBAC is …

…enabled (#567)

When RBAC has been enabled under v1.15.1, persistent volumes can be created using persistentvolumeclaims.

However after the persistentvolumeclaim is deleted, hostpath provisioner deletes the backing store, but fails to delete the persistent volume due to a 'forbidden' error, e.g.

Adding the `delete` verb to the ClusterRole for persistentvolumes.

microk8s-resources/actions/storage.yaml

@@ -73,6 +73,7 @@ rules:
   - update
   - watch
   - create
+  - delete
 - apiGroups: [""]
   resources:
     - events