text: Title: Do not leak GCE PD in federation tests
  Body: Our ci tests started failing sometime yesterday (https://k8s-testgrid.appspot.com/sig-federation) with errors such as:
  ```
  Error: 1 leaked resources
  [ disks ]
  +prow-us-central1-f-dyn-pvc-d11b7df7-7eed-11e7-a35f-42010a80000a  us-central1-f  10       pd-standard  READY
  ```
  
  @madhusudancs pointed out that we have always been leaking the GCE PD provisioned using Dynamic provisioning, we probably updated our tests now to catch it.
  
  ci tests on HEAD and all release branches are now failing.
  
  cc @kubernetes/sig-federation-bugs 