ChildSpec: add COLLECT_AFTER_HW_TEST

Child builds thus marked should not block the start of hardware tests.

BUG=chromium:1108925
TEST=generate

Change-Id: I1049c93c091eefef1d52c55e272255f15b0c12c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2399258
Reviewed-by: David Burger <dburger@chromium.org>
Commit-Queue: LaMont Jones <lamontjones@chromium.org>
Tested-by: LaMont Jones <lamontjones@chromium.org>
2 files changed