Make the udid variable optional in management commands when the env is set
Make the udid variable optional in management commands when the env is set

Summary: This makes the cases a lot clearer now, including that args override env

Reviewed By: c-ryan747

Differential Revision: D20556817

fbshipit-source-id: 0edff340d3f1ce171b60ba5e76746f06f4a96a32

facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl