As the Vikings prepare to open the exhibition season with a game against the Houston Texans, young quarterback J.J. McCarthy is expected to see some action. How much will he play on Saturday afternoon at U.S. Bank Stadium? That’s the part that head coach Kevin O’Connell isn’t ready to confirm. “We’ve got that plan in place,” O’Connell said. “I have not talked to him about it. We’re so day to …