devtools/v23/internal/test: output "uncaught" test errors to stderr.
devtools/v23/internal/test: output "uncaught" test errors to stderr.

This is related to: https://github.com/vanadium/issues/issues/100

Change-Id: I958f1b1683fe00233f6fd3347555e3634a267726

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