By David Shepardson WASHINGTON (Reuters) – U.S. Labor Secretary Marty Walsh kept railroads and unions at the bargaining table for 20 hours, fueled by sandwiches and baked ziti, to clinch a make-or-break labor deal early Thursday. With President Joe Biden insistent and the U.S. economy in the balance, there was no room for failure and no time for a traditional style of negotiations with rounds of document exchanges, he said in an interview. “I wanted to get this deal done,” said Walsh, a former Boston mayor who canceled a trip to Ireland and speech to Irish legislators to broker the talks. Afte…