Reuters By Julie Zhu and Kane Wu HONG KONG (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 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 like horticulture. It’s a far cry from the height of Ma’s…