https://github.com/knative/serving/issues/3913

What version of Knative?
HEAD

Expected Behavior
On shutdown signal, controller and networking/istio shut down their embedded controllers and then return from main()

Actual Behavior
controller and networking/istio fall off main() on shutdown signal giving embedded controllers no chance to shut down cleanly

Steps to Reproduce the Problem
Start either controller, let initialize, ^C, watch logs.

See sister bug in knative/eventing#1109