By Elizabeth Piper KYIV (Reuters) – It’s the five years spent serving in the Ukrainian army that drives Deputy Prime Minister Iryna Vereshchuk’s passion to secure the release of every single prisoner of war being held in Russia. Now in charge of negotiating prisoner swaps with Russia and humanitarian corridors out of besieged cities, Vereshchuk, 42, fights back tears as she describes the treatment of some women soldiers she has managed to bring back to Ukraine. It is a brief glimpse of the toll her work is taking, but is quickly replaced by her overriding anger over the Russian invasion and th…