UFC's Mark Hunt -- Demands HALF Of Brock's UFC 200 $$$ ... He's A 'Cheater'

Mark Hunt is FURIOUS over Brock Lesnar's potential failed drug test ... DEMANDING half of B.L.'s UFC 200 winnings ... or he's bolting the UFC. Hunt laid it all out on his website Friday night ... saying, "I've told Dana I want half of Brock's…