Catch the exception thrown in xcrun

Summary: Catch the exception thrown in xcrun, which will occur for linux machines and in the cases when Xcode command line toolchain is not installed.

Reviewed By: passy

Differential Revision: D15621368

fbshipit-source-id: f3044cee6f7a4b5ba927a33003f9690c1fe31586

src/dispatcher/iOSDevice.js

@@ -132,7 +132,8 @@ function getActiveSimulators(): Promise<Array<IOSDeviceParams>> {
             name: simulator.name,
           };
         });
-    });
+    })
+    .catch(_ => []);
 }
 
 function getActiveDevices(): Promise<Array<IOSDeviceParams>> {