MADRID (Reuters) -Britain’s Defence Secretary Ben Wallace on Wednesday called on Russia to let Ukraine export its grain to help countries where grain scarcity could trigger hunger. Russia must “do the right thing”, Wallace told reporters in Madrid where he met his Spanish counterpart Margarita Robles, and open a grain corridor from Ukraine’s Black Sea ports. On Thursday, Russian Deputy Foreign Minister Andrei Rudenko said the country was ready to provide a humanitarian corridor for vessels carrying food to leave Ukraine, in return for the lifting of some sanctions, the Interfax news agency rep…