By Avi Creditor The U.S. goalkeeper is a backup at Arsenal, and just like his main competition for World Cup minutes did before him, he’s relying on training to be sufficient. For the first time representing his new club, Matt Turner entered a U.S. men’s national team camp getting a version of the question that one of his compatriots and his chief competition for World Cup minutes has heard for quite some time. It goes something like: Can you really stay in form and sharp if you’re not getting regular matches? That question had been lobbed at Zack Steffen for the last two years, as he deputize…