Creating 2 new build jobs one dependent on the other by "trigger parameterized build on other projects" or "Build after other projects are built". This results in the relationship being observed here:

Trigger the upstream build (in our case takes hours to complete) and observe the downstream relationship within the pipeline view:

Now reload configuration from disk, and reload the build pipeline view:

The resulting effects are as follows:
Hipchat notification for upstream job (start) is sent
CLI Exec on swarm slave runs and completes
Hipchat notification for upstream job (complete) is never sent
Downstream build job is never executed.