Rinse and pat dry the pork butt. In a small bowl mix together all of the ingredients for the spice rub. Coat the pork completely with the spice mixture and rub it into meat. Put the roast into a roasting pan or a high sided casserole dish with a lid. Pour enough chicken stock into the pan to come about 1/2-inch up the sides. Cover the pan tightly with foil or lid and put in the oven. Roast the pork until meat is completely tender and pulls apart very easily, about 4 1/2 to 5 hours. Remove from oven and allow to rest for 10 minutes before shredding the pork from the bone.
For the Slaw: While the pork is roasting combine the cabbage with the carrots and onion in a large bowl. In small bowl whisk together the remaining ingredients. Pour the dressing over the slaw and toss to combine. Refrigerate for at least 1 hour and up to overnight. Season with more salt and pepper, to taste, before serving.
Preheat the oven to 250 degrees F.
Slice the dinner rolls in half and put on a sheet pan to warm in a low oven. When ready to assemble the po' boys, put some shredded pork on bottom of each roll, top with some BBQ sauce and finish with a heaping spoonful of the slaw. Cover with the roll tops and serve immediately.