By Simon Lewis ON THE ROAD TO SIVERSK (Reuters) – As artillery fire booms nearby, Dmytro looks up and listens. “That’s ours,” notes the 28-year-old, deputy commander of his infantry unit, perched on the edge of a deep earth bunker covered with logs and sandbags near the road to the frontline town of Siversk in eastern Ukraine. “This sound calms us down,” he says. “Right now it’s more of our artillery than theirs, so it’s good. But there might be incoming soon.” Light machine guns are at the ready atop an embankment, as the unit, which recently pulled back from the now-occupied city of Lysychan…