common/iotools: Cleanup/Fix deadlinereader test.
common/iotools: Cleanup/Fix deadlinereader test.

BUG=None
TEST=None
R=iannucci@chromium.org

Review URL: https://codereview.chromium.org/1359943005

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