Automatic merge from submit-queue (batch tested with PRs 41814, 41922, 41957, 41406, 41077)
pv_controller: Do not report exponential backoff as error.
It's not an error when recycle/delete/provision operation cannot be started
because it has failed recently. It will be restarted automatically when
backoff expires.
This just pollutes logs without any useful information:
```
E0214 08:00:30.428073 77288 pv_controller.go:1410] error scheduling operaion "delete-pvc-1fa0e8b4-f2b5-11e6-a8bb-fa163ecb84eb[1fbd52ee-f2b5-11e6-a8bb-fa163ecb84eb]": Failed to create operation with name "delete-pvc-1fa0e8b4-f2b5-11e6-a8bb-fa163ecb84eb[1fbd52ee-f2b5-11e6-a8bb-fa163ecb84eb]". An operation with that name failed at 2017-02-14 08:00:15.631133152 -0500 EST. No retries permitted until 2017-02-14 08:00:31.631133152 -0500 EST (16s). Last error: "Cannot delete the volume \"11a4faea-bfc7-4713-88b3-dec492480dba\", it's still attached to a node".
```
```release-note
NONE
```
@kubernetes/sig-storage-pr-reviews
It's not an error when recycle/delete/provision operation cannot be started
because it has failed recently. It will be restarted automatically when
backoff expires.
PV controller should not use Controller.Requeue, as as it is not available in
shared informers. We need to implement our own work queues instead where we
can enqueue volumes/claims as we want.
