One day after his right knee buckled, Astros outfielder J.D. Martinez was placed on the 15-day disabled list with a sprained right knee as Fernando Martinez was activated from the DL Saturday. “I don’t think the injury to J.D. is going I keep him out very long, but we want to be conservative with it,” Astros general manager Jeff Luhnow said. “So four-five days of nothing and taking swings and rehab and so forth and he’ll be ready to go.” The Astros also activated lefthanded reliever Travis Blackley from the DL. Fernando Martinez was expected to arrive at Minute Maid Park in time for the second game of the three-game [...]