Dodgers manager Dave Roberts explained why he used Brusdar Graterol as the opener and Andrew Heaney out of the bullpen in Thursday’s game. In Thursday’s 5-2 win over the Padres, Dodgers manager Dave Roberts opted to use Brusdar Graterol as an “opener,” with Bazooka throwing the first inning and Andrew Heaney, normally a starter, coming out of the bullpen starting with the second inning. After the game, Roberts was asked about his reasoning for using Graterol and Heaney in that way, and his answer suggests it was all about Heaney, as reported by Jim Alexander in the Orange County Register.…