Show stdout/stderr in tool_test.sh when a copybara invocation fails
Show stdout/stderr in tool_test.sh when a copybara invocation fails

This helps debugging when Copybara returns non-zero unexpectedly
during development.

Change-Id: Ia61070d16abb279accabbebbdc376b5123796836

google/copybara,google/copybara,google/copybara