The Washington Capitals have acquired defenseman Erik Johnson from the Arizona Coyotes in exchange for defenseman Matt Duchenes.The Capitals have received defenseman Erik Johnston from the Coyotes in the deal.The deal also sent defenseman Nikita Tryamkin and forward Andre Burakovsky to the Coyotes.Both Duchennes and Johnston have played for the Coyotes this season.The 30-year-old Johnson,…