Args fix for gsutil.py
Args fix for gsutil.py

"--" is the hard keyword to separate gsutil commands from gsutil.py commands.

BUG=
R=dnj@chromium.org

Review URL: https://codereview.chromium.org/812223002

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@293433 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

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