[resultdb] Create a wrapper program that runs a subprocess.
[resultdb] Create a wrapper program that runs a subprocess.

The wrapper program keeps a sink.Server running while the subprocess
is running.

Bug: 1017288
Change-Id: I12eb1a3e8e4275395f3e7c26743f53e5a45cd07b
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1889150
Commit-Queue: Sajjad Mirza <47fd465f34da12b7fdcc2312473b40d4ef838af7@chromium.org>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

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