Make delete test less flaky

Instead of arbitrary wait times it now:
* Verifies that the index operation worked in the first place
* Waits *up to* 75 seconds for the delete but typically catches it after
one or two.  75 is used because that is a nice long timeout for beta in
case its job queue is backed up.

Change-Id: I694d845b25ec06de6a29d71f468b319f235c5344