The A’s just announced that infielder Adam Rosales, who’s well-liked by management and the coaching staff, will open the season on the disabled list with a strained left intercostal. With Rosales, who was hurt in Monday’s game, on the DL and Jemile Weeks in minor-league camp, the roster is taking shape. In all liklihood, Jed Lowrie will be the No. 1 shortstop — the A’s were considering having Hiro Nakajima start with Triple-A Sacramento. Scott Sizemore and lefty-swinging Eric Sogard would platoon at second.