Microsoft on Thursday reported strong fourth-quarter earnings on the back of its fast-growing cloud computing business, stoking optimism that the once-stagnant company has found a new groove.The results were the clearest sign yet that the strategy put in place by Chief Executive Satya Nadella when he assumed the top job in 2014 is paying off. He has shifted the company's focus away from a dying personal computer software business and reinventing it as a provider of cloud computing and subscription-based software.