[bbagent] Pick a better milo hostname.
[bbagent] Pick a better milo hostname.

I think we'll need to add a new section to Build.Infra for this.
Previously kitchen got this via a CLI flag.

TBR=nodir@chromium.org, tandrii@chromium.org

Bug: 1010744
Change-Id: I580e15d5d622d7c2e801f8b64643c7af458282db
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1837372
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

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