Horse racing is most commonly defined by what happens at the finish line.But long before any of that, before the gates open and the bets are placed, the real work is already done.For assistant trainer David Carroll, it starts hours before sunrise.Get up around 3:30 arrive at work at 4 you walk down the shed row to see whos eating and not, who looks well and not the whole morning is programmed. 5:30 a.m., the track opens up it takes a village, an…