Refactor genericScheduler and signature of preemption funcs
- remove podNominator from genericScheduler
- simplify signature of preemption functions
Make Preempt() private
- Add a defaultpreemption PostFilter plugin
- Make g.Preempt() stateless
- make g.Preempt() stateless
- make g.getLowerPriorityNominatedPods() stateless
- make g.processPreemptionWithExtenders() stateless