Automatic merge from submit-queue (batch tested with PRs 38505, 41785, 46315)

Fix provisioned GCE PD not being reused if already exists

@jsafrane PTAL 

This is another attempt at https://github.com/kubernetes/kubernetes/pull/38702 . We have observed that `gce.service.Disks.Insert(gce.projectID, zone, diskToCreate).Do()` instantly gets an error response of alreadyExists, so we must check for it.

I am not sure if we still need to check for the error after `waitForZoneOp`; I think that if there is an alreadyExists error, the `Do()` above will always respond with it instantly. But because I'm not sure, and to be safe, I will leave it.