Adm. Bill McRaven is a bad-ass — and fount of good advice. Head of the Joint U.S. Special Operations Command, he is a 36-year SEAL who has been at the tip of the spear in the war on terror since 2001. He has commanded a squadron in the fabled Naval Special Warfare Development Group, better known as SEAL Team Six, and he oversaw planning and execution of the raid that killed Osama bin Laden. He is also the most mysterious and guarded Navy four-star. While Admirals Greenert, Gortney, Locklear and company frequently appear in the media and before Congress, McRaven shies…