By Marianna Parraga HOUSTON (Reuters) - A long-awaited sale hearing expected to complete a U.S. court-organized auction of shares in the parent of Venezuela-owned U.S. refiner Citgo Petroleum kicked off on Monday, with bidders and creditors locked in a bitter dispute over who should win. The Delaware court is hearing testimony from involved parties, witnesses and experts in the four-day showdown before Judge Leonard Stark selects a final winner. At stake is the future of the seventh largest U.S. refiner ...