By Pete Schroeder WASHINGTON (Reuters) – Large U.S. banks are optimistic they will receive a clean bill of health from the Federal Reserve this week, freeing them up to distribute billions of dollars in excess capital to investors. The central bank on Thursday will release the results of its annual bank “stress tests” which assess how much capital banks would need to withstand a severe economic downturn. The annual exercise, introduced following the 2007-2009 financial crisis, is integral to banks’ capital planning, dictating how much cash they can return to shareholders in the form of dividen…