Use "set noparent" in testing/buildbot/OWNERS to make it effective

testing/OWNERS has * in it.

Example CL where this made a difference: https://codereview.chromium.org/246623009/

BUG=none
R=sky@chromium.org

Review URL: https://codereview.chromium.org/289863006

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@271641 4ff67af0-8c30-449e-8e8b-ad334ec8d88c