Affects Version/s: None
Fix Version/s: 3.0.0
Currently, the SchedulingPlacementSet is very confusing. Here're its responsibilities:
1) Store ResourceRequests. (Or SchedulingRequest after
2) Decide order of nodes to allocate when there're multiple node candidates.
3) Decide if we should reject node for given requests.
4) Store any states/cache can help make decision for #2/#3