this is necessary for portage-based builds which change the
chroot. You must pass --chroot to the run_remote_tests in this
case.
Review URL: http://codereview.chromium.org/588010
Don't punish the good people trying to write python-only autotests by
requiring them to sit through a long build_autotest run to test
every change. run_remote_tests and build_autotest both update
the chroot copy now.
Review URL: http://codereview.chromium.org/578027
