By David Shepardson and Lisa Baertlein DETROIT/LOS ANGELES (Reuters) -Biden administration officials, racing to avert a potential rail shutdown that could disrupt cargo shipments and impede food and fuel supplies, hosted labor contract talks on Wednesday as one of the smaller unions involved in the dispute rejected a deal. Railroads including Union Pacific, Berkshire Hathaway’s BNSF and Norfolk Southern have until a minute after midnight on Friday to reach tentative deals with three holdout unions representing about 60,000 workers before a work stoppage affecting freight and Amtrak passenger r…