By Christoph Steitz and Thomas Escritt FRANKFURT (Reuters) -Germany’s largest power producer RWE has agreed to buy Con Edison’s Clean Energy Businesses for $6.8 billion, nearly doubling RWE’s renewables portfolio in the United States, the world’s second-biggest renewables market. The purchase will be partly funded by RWE issuing a $2.43 billion convertible bond to a Qatar Investment Authority unit, through which the QIA will become a 9.1% shareholder in RWE. Con Edison said it was scrapping plans to issue up to $850 million in new shares this year and withdrawing equity guidance for the next t…