Force UITests to run on mainthread
Force UITests to run on mainthread

Summary: Xcode 8 GM executes UITests with this value set to YES. So doing the same

Reviewed By: lawrencelomax

Differential Revision: D3835432

fbshipit-source-id: 9cb5af19af2a91d06f482ae85d7d72fcab25b8cf

facebook/FBSimulatorControl,bootstraponline/FBSimulatorControl,plu/FBSimulatorControl,facebook/FBSimulatorControl,bootstraponline/FBSimulatorControl,StevenUpForever/FBSimulatorControl,StevenUpForever/FBSimulatorControl,bootstraponline/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,ichu501/FBSimulatorControl,facebook/FBSimulatorControl,plu/FBSimulatorControl,bootstraponline/FBSimulatorControl,plu/FBSimulatorControl,plu/FBSimulatorControl,StevenUpForever/FBSimulatorControl,StevenUpForever/FBSimulatorControl