In 2007, Def Leppard’s summer shed tour with Styx and Foreigner grossed about a half-million dollars per show and played to 13,000-18,000 fans per stop.  Those are big numbers for a headlining band whose biggest success came more than 20 years ago.  This summer, Def Leppard is touring with the even-better matchup of Poison and Cheap Trick, and now, the mostly-British rockers might find a new faction of fans amid the packs of long-haired’80s holdovers and thirtysomething women who spent their prom nights singing along to “Pour Some Sugar on Me”: country-music listeners.