Fix the update e2e test to remove a race.

See #2361 

The problem occurs when we scale down, and the pod doesn't get deleted quick enough, and then disappears underneath us while we're trying to introspect it.

Solved in two ways:
  * Make a failed get not fail the test
  * Explicitly look for a match to the expected number of replicas.

OK, that's what I thought. Clearly I'm failing at my life goal of not learning any bash. ;)