The Port of Los Angeles is seen at dawn in San Pedro, California in this August 20, 2014 file photo. Credit: Reuters/Lucy Nicholson/Files **********************************LOS ANGELES (Reuters) - The chief labor negotiator for shippers and terminal operators at 29 U.S. West Coast ports raised the ante in contract talks with the dockworkers' union on Wednesday, warning that ports plagued by chronic cargo slowdowns were days away from complete gridlock.But union officials downplayed the potential for shutdowns, suggesting management was exaggerating a crisis as a late-hour negotiation ploy, and countered that the two sides were already close to a settlement.The contract...