PR for [REEF-44]:Remove usage of artificial nCLREvaluators constrain

This is for [REEF-44]. Currently.net bridge java driver assumes that evaluators are only requested during startup or when evaluator fails, this is a unnecessary constrain that blocks the scenario where elastic evaluaors allocation is needed. This commit removed that man-made constrain.
It may be better to use `running` or `total running`, instead of `total running running`