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.
This implements pv_controller to exponentially backoff
when deleting a volume fails in Cloud API. It ensures that
we aren't making too many calls to Cloud API
Gluster provisioner is interested in pvc.Namespace and I don't want to add
at as a new field in VolumeOptions - it would contain almost whole PVC.
Let's pass direct reference to PVC instead and let the provisioner to pick
information it is interested in.
