Replace <locale>.numCores with <locale>.maxTaskPar where appropriate.

Replace numCores with maxTaskPar everywhere in the module code. This will cause us to compute  parallelism based on what the tasking layer says it can achieve, rather than on what we think we have available in terms of hardware.

While here, I also changed numCoreTasks to numSublocTasks in DefaultRectangular.chpl, to reflect what I think we're actually computing there.