SAN ANTONIO — For a 21-year-old who has never played above Class AA and is still shaking off the negativity that comes with a 50-game suspension for failing a drug test, Jonathan Singleton is very self-aware. The 6-2, 235-pound first baseman knows he has accomplished little in pro baseball, despite being the No. 2 prospect in the Astros’ farm system, according to Baseball America. Singleton acknowledges spending nearly two months in extended spring training in Kissimmee, Fla., wasn’t ideal for the next stage of his career. Hitting three home runs during his three comeback games for low A Quad Cities was a thrill. But a .241 batting average with 13 [...]