cq.cfg: enable experimental swarming builders
cq.cfg: enable experimental swarming builders

R=estaab@chromium.org, vadimsh@chromium.org
BUG=622093

Review-Url: https://codereview.chromium.org/2087053002

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py