Ebola appeared out of nowhere. A delayed diagnosis, a patient’s death and two infected nurses reflected a cascade of mishaps while “Presby,” as the hospital charmingly is called, became linked to a fearsome disease and global exposure of the worst kind. This has been a hospital under siege. Ever since the night when a man from Liberia entered the emergency department — one that, as few know, is run by an outside contractor, not the hospital — a new reality has altered Presbyterian’s course.