Do not fail test run if deleting working directory failed.
Do not fail test run if deleting working directory failed.

Summary:
Some unknown service will add additional simulator to the
simulator set created by fbxctest, so fbxctest will fail delete the
working directory because it has no permission on simulator added
by other serivces. In this case we just print an error message but not
fail the test run.

Differential Revision: D21345476

fbshipit-source-id: 7ce9976110ab30dc58730f2d39b631d033ce1097

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