Members of Tesla’s board are scrambling to control a chief executive who some directors think is out of control. Elon Musk, the Palo Alto company’s co-founder and CEO, stirred up a public storm by announcing on Twitter last week that he wanted to turn Tesla into a private company. In recent days, according to people familiar with the matter, some of his fellow board members delivered a stern message: Stop tweeting. Musk hasn’t heeded that advice. He has continued to post messages on Twitter, publicly plotting the company’s strategy and in some cases making assertions of dubious accuracy.