Minor cleanups to CL 561635's test for better debuggability
when it crashes. In a separate CL so that it's clear this CL is
not changing the code under test.
Change-Id: I12b72ae538f8454b5c382127eafd766c22c69b67
Reviewed-on: https://go-review.googlesource.com/c/go/+/571799 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>