Elon Musk is finally getting his adult supervision. Robyn Denholm, finance chief at Australian telecom operator Telstra, will move from her boardroom seat at Tesla to the head of the table – and oversee the $60 billion electric-car maker’s erratic chief executive full-time. She will have to get tougher, though. Having an independent chair is a plus, even if it was forced on Musk by the U.S. Securities and Exchange Commission. A regulatory settlement followed his excessively confident public statements about a potential deal to take Tesla private. The company has plenty on its plate, from the hands-on task of ramping