Automatic merge from submit-queue (batch tested with PRs 36888, 38180, 38855, 38590)

Fix variable shadowing in exponential backoff when deleting volumes

While https://github.com/kubernetes/kubernetes/pull/38339 implemented exponential backoff on
volume deletion, that PR suffers from a minor bug when error thrown on volume deletion is anything other than `VolumeInUse` errors - in which case exponential backoff will not work.

This PR fixes that. This PR also makes unit tests more deterministic because exponential backoff changed the way operations are permitted.

CC @jsafrane @childsb @wongma7