Add test coverage for supported child thread terminations

Add tests verifying that StepCount, ScoreCalculationCount and time-based terminations applied to child threads work as expected.

The main question is whether the first child thread that reaches the termination condition should terminate all siblings or whether the parent termination should wait until all children have reached the condition. The question gets a little more complicated in the situation when runnablePartThreadLimit is lower than partCount and child thread's CPU time becomes different from the real time.

BestScore(Feasible)Termination is not supported. We might want to add a negative test for such a configuration.