cv: parallelize two distinct ds.Put during run creation.
cv: parallelize two distinct ds.Put during run creation.

As you know,
  All CS problems can be solved by introducing layers of abstraction,
  except performance which is solved by removing them.

eventbox, and in turn dsset, are very nice encapsulations,
but it means they hide datastore.Put(). While I could break this
encapsulation, it's easier to just make 2 concurrent calls.

R=qyearsley, yiwzhang

Bug: 1156241
Change-Id: Idd24b4c431c4e75470d35b06b4600d68e1bedf7f
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2612178
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>

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