AUGUSTA, Ga.—After a tumultuous final round at last year’s Masters where he coughed up a five-shot lead on the back nine and found himself in a playoff, Rory McIlroy’s caddie reminded him of one important truth: They would have absolutely taken this scenario before the tournament started.  A similar pep talk was in order before Sunday’s final round. McIlroy might have been the defending champion, but he was teetering on the brink of collapse once again.  A superstar with a knack for making everything as difficult as possible for himself, the 36-year-old from Northern Ireland held a historic six-stroke lead…