Iowa hosted its first-ever MLB game last night on a specially constructed field next to the real-life  “Field Of Dreams” movie set. The Chicago White Sox beat the New York Yankees 9-8 with a walk-off homer in the 9th.  But it was the opening that was even better.   Kevin Costner led the players through the cornfield and onto the field.  And then Costner addressed the crowd.   For an added old-school touch, both teams wore retro uniforms and even the scoreboard was changed . . . manually.  The MLB commissioner says they’ll return for another game next year.