BELFAST, — Paul Sharkey lived through decades of sectarian violence between Protestant and Roman Catholic communities known as “the Troubles,” but thought that bloody phase of Northern Ireland’s history was over. Then, on Wednesday evening, he heard a loud noise near his house on the Antrim Road in Glengormley, on the northwest edge of Belfast. When he looked out of his window, a burning van was hurtling toward his home. “It was heading toward me — I was panicking,” Sharkey, 71, said.