Use String Constants for FBiOSTarget Keys
Use String Constants for FBiOSTarget Keys

Summary: Constants are good, lets use them.

Reviewed By: marekcirkos

Differential Revision: D4778718

fbshipit-source-id: 00e869d14ee5641332779dd4a50e6acf721961fe

StevenUpForever/FBSimulatorControl,StevenUpForever/FBSimulatorControl,facebook/FBSimulatorControl,StevenUpForever/FBSimulatorControl,plu/FBSimulatorControl,facebook/FBSimulatorControl,StevenUpForever/FBSimulatorControl,facebook/FBSimulatorControl,plu/FBSimulatorControl,plu/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,plu/FBSimulatorControl