cv: Keep uploader information in snapshot.
cv: Keep uploader information in snapshot.

This is needed for notifying the uploader in case a new patchset run
fails.

R=yiwzhang

Bug: 1242951
Change-Id: Icea8d3a28f53b3cb4d288c1591c63f8ff40ec123
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3946101
Commit-Queue: Roberto Carrillo <b31161e510fbb37f8f70fdcde11530d2bae88470@chromium.org>
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

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