Add repeated ChildSpec configuration to orchestrator.

Add a repeated ChildSpec configuration to orchestrator intended to allow
fo the use case of specifying children that the orchestrator should not
wait for or that should be able to live on if the orchestrator itself
exits. This is intended to allow the use cases of testing new builders
without holding up the CQ run itself. The goma RBE builder is such an
example. We'd like to see what is going on with it but we don't want the
orchestrator to sit there and wait for it.

BUG=None
TEST=None

Change-Id: If7ee84047174f21ab0fb04f415f6cb5d03febc5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2041704
Commit-Queue: David Burger <dburger@chromium.org>
Tested-by: David Burger <dburger@chromium.org>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
3 files changed