Slipknot’s Knotfest will be teaming up with Hellfest for a “Knotfest Meets Hellfest” mini-festival in Clisson, France. The event will take place on June 20, one day before Hellfest Open Air officially kicks off. The following bands will perform: Slipknot, Rob Zombie, Papa Roach, Ministry, Sick Of It All, Sabaton, Amon Amarth, Powerwolf, Behemoth, and…