text: Title: Add experimental node upgrade test asserting service continues to function
  Body: This puts in place a `[Feature:ExperimentalNodeUpgrade]` test that asserts that a service continues to respond across an upgrade.  Right now it doesn't work, so I shuffled around labels to keep current functionality until the more rigorous test is stable.
  
  I also removed some dead test code (`kube-push`) and added some `TODO`s for myself to come back to.
  
  Work toward #15131.
  
  cc @mikedanese 
  