devtools/jiri-test: better handle "package build failure" in tests.
devtools/jiri-test: better handle "package build failure" in tests.

This is to better handle failures like this:
https://veyron.corp.google.com/jenkins/job/vanadium-presubmit-test/ARCH=amd64,OS=linux,TEST=vanadium-go-test/11170/console

Change-Id: Ifb193f0c17c69d293a0f2929e917249dee95219a

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools