HONG KONG, Nov 5 (Reuters) - This was supposed to be Jack Ma's finest hour: a year ago to the day, his Ant Group was meant to go public in a $37 billion blaze of glory. Instead Beijing reined in his empire, abruptly clipping the wings of corporate China's biggest star. Now, to the cautious cheer of investors, the billionaire Alibaba (9988.HK) e-commerce tycoon is taking his first tentative steps back on to the global stage with a low-key trip to Europe where he's cultivating hobbies like horticulture. It's a far cry from the height of Ma's statesman-like powers in...