By Gavin Jones, Giuseppe Fonte and Angelo Amante ROME (Reuters) -Italian head of state Sergio Mattarella was re-elected for a second term on Saturday, with party chiefs asking him to carry on after a week of fruitless, often fraught voting in parliament to choose a successor. Relieved party chiefs thanked 80-year-old Mattarella for agreeing to remain, but the failed attempts to replace him during seven rounds of balloting have left deep scars, with potentially dangerous repercussions for political stability. Nonetheless, financial markets are likely to react positively to the status quo, which…