Use alternative paths if cwd = /
Use alternative paths if cwd = /

Summary:
If the idb companion for a device is started with the cwd = / then it'll crash on startup due to a lack of permission to create /idb-...

Using /tmp/... as a fallback

Reviewed By: lawrencelomax

Differential Revision: D20159456

fbshipit-source-id: 86f8d6ccbe775597459a2e6cabc418ebc7755fe6

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