FBI agents have recovered a black glove from a roadside near Nancy Guthrie’s house — potentially a major clue in the search for the masked thug who is suspected of abducting the 84-year-old woman, The Post can reveal. Detectives found the clothing item, which resembles the pair worn by the armed perpetrator caught on video, about one and a half miles from the home of “Today” show host Savannah Guthrie’s mother.