Try a maximum concurrency of 1.
Try a maximum concurrency of 1.

Travis still running OOM, might as well try the base case.

BUG=

Review URL: https://codereview.chromium.org/1595663003 .

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go