Gruff actor Dabney Coleman made life miserable for secretaries Dolly Parton, Jane Fonda and Lily Tomlin as their nasty boss in 9 to 5, but pals claim he went to his grave happy as a clam after guest-starring on hit TV show Yellowstone, RadarOnline.com has learned. In his final role, the 92-year-old Emmy winner, who died at his Santa Monica home May 16, played the dying dad of Kevin Costner’s rancher John Dutton in a season 2 flashback. “Dabney knew Yellowstone would be his swan song as an actor,” a pal revealed to the Globe. “And he was thrilled to get the part. And he didn’t have to play a cr…