Music superstar and fashion and beauty mogul Rihanna has joined Jay-Z and Kanye West on Forbes’ Billionaires List. The 34-year-old Rihanna has assets worth $1.7 Billion, according to Forbes. Her stakes in the Fenty Beauty cosmetics line and the Savage X Fenty lingerie business helped make her Barbados’ first billionaire. The musician-turned-cosmetics mogul became the…