fair share scheduler causes unnecessary preemption under some conditions

When the cluster hits speculative cap - JobInProgress does not speculate any more. however FairShare Scheduler continues to believe that tasks need to be speculated.

Under such conditions, FS Scheduler will start preempting repeatedly (because from it's perspective - certain jobs are not getting the slots they deserve (for speculative tasks)).

There may be other reasons for excessive preemption as well - this one stood out clearly.