WESTERLY, R.I. — Like a dress rehearsal for a show that no one wants to see, a simulated oil spill brought more than 100 people to Westerly Wednesday and Thursday to practice their parts.Organized by Coast Guard Sector Southeastern New England (which extends from Watch Hill to Cape Cod and the Islands) and dubbed the Watch Hill Spill, the two-day drill brought together 111 people from 17 federal, state and local agencies to practice their coordinated response.