Reba McEntire and Brooks & Dunn are getting an earlier start to their Las Vegas engagement.  The country stars have added three new dates to their upcoming run of collaborative shows at The Colosseum at Caesars Palace, the shows launched Wednesday night.  “Reba, Brooks & Dunn: Together in Vegas,” is being billed as a “one-of-a-kind country Music residency.”  It also marks a reunion for the duo, who split up five years ago.