jiri-test/internal/test/prod.go: print more info about failed commands
jiri-test/internal/test/prod.go: print more info about failed commands

To make it easier to diagnose issues with vrpc commands failing or
timing out.

Change-Id: Ib32175aa67ace9c5d97fb1f27b1cb3e9d0a36762

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