It’s been 30 years since director Ridley Scott made a science-fiction film, so his return to the genre created a lot of excitement. The anticipation was warranted because Scott is a fine craftsman and his early science-fiction efforts, “Alien” and “Blade Runner,” are classics. With “Prometheus,” Scott is back in the “Alien” universe, telling a story that takes place before the events of his original 1979 movie.