Made gsutil.py truly transparent
Made gsutil.py truly transparent

The previous version was modifying gsutil output by adding a
stacktrace upon non-zero return code, which broke existing code.

BUG=400871
R=hinoka@chromium.org

Review URL: https://codereview.chromium.org/822093002

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@293501 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools