This implements Bulk volume polling using ideas presented by
justin in https://github.com/kubernetes/kubernetes/pull/39564
But it changes the implementation to use an interface
and doesn't affect other implementations.
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.