* STOXX 600 up almost one percent; Auto shares leap 2.2 percent. : LONDON (Reuters) - European auto shares surged more than 2 percent on Monday as news of a U.S.-Mexico agreement on NAFTA added to the bullish sentiment generated by U.S. Federal Reserve chairman Jerome Powell’s market-friendly speech. A British public holiday thinned trading volumes across the region but European markets opened broadly firmer after Powell late last week affirmed the U.S. central bank’s current gradual pace of rate hikes. The comments sent Wall Street to record highs on Friday.