By Francesco Canepa and Giselda Vagnoni FRANKFURT/ROME (Reuters) – The European Central Bank seems almost certain to face a test of its resolve to rein in excessive bond yields in coming weeks as the euro zone’s biggest debtor, Italy, heads for elections that a rightist bloc with a eurosceptic past is expected to win. The ECB, in an attempt to cushion the impact of rising borrowing costs on Italy and other parts of the euro zone’s south, said last week that it would intervene in support of countries whose debt comes under market pressure through no fault of their own. With the interest premium…