One of rap's biggest festivals is underway from East Rutherford's MetLife Stadium, where the packed lineup features Nicki Minaj, Rick Ross and MMG, Young Jeezy, Meek Mill, A$AP Rocky, Azealia Banks and more. Big, unannounced guest spots are pretty much the norm -- Drake came out for Lil Wayne's set last year, for example -- so it's probably worth hitting ...