GTTF: make sharding_supervisor.py use --brave-new-test-launcher

BUG=236893
R=maruel@chromium.org

Review URL: https://codereview.chromium.org/39213002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231046 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231046