By Isla Binnie and Gavin Jones ROME (Reuters) - Italians voted on Sunday in regional ballots which will test whether the country, tired of economic stagnation and austerity, is also wearying of Matteo Renzi's nine-month old coalition government. Renzi's popularity peaked in June shortly after a landslide victory in European parliament elections, but his ruling party has been steadily slipping lower in opinion polls since, as the economy stutters and joblessness remains stubbornly high. ...