Also move the GC stress configuration from the buildbot to the test runner.

BUG=
R=jkummerow@chromium.org, mvstanton@chromium.org

Review URL: https://codereview.chromium.org/141653008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18708 ce2b1a6d-e550-0410-aec6-3dcde31c8c00