Davey Johnson will manage the Nationals for the rest of this season and 2012, ESPNChicago’s Nick Friedell reports. It’ll be the first managerial gig for the 68-year-old Johnson since his two-year stint with the Dodgers ended in 2000.  The one-time World Series winner with the Mets in 1986 has a career 1,148-888 record in 14…