Added all remaining SchedulerDriver Methods

Added the followings to project:
* DeclineOffer() + unit test
* ReviveOffers() + unit test
* ReconcileTasks() + unit test
* ReconcileTasks() + unit test
* RequestResources() + unit test

@nqn There is already code for executor tests (see executor_test.go).  But there could be more integrative tests added to exercise executor driver, executor, and master communication.