By Bruno Federowski and Miguel Gutierrez BRASILIA, Dec 22 (Reuters) - The Mexican peso hit a nine-month low on Friday, battered by a U.S. tax overhaul and domestic corruption scandals that boost a leftist front-runner's chances in next year's elections. U.S. President Donald Trump signed sweeping tax legislation into law on Friday, slashing the U.S. corporate rate to 21 percent from 35 percent beginning on Jan. 1. The bill has prompted worries in Mexico that the country could los