Bug 1082935 - Fixing scope problem with bluetooth transfer device name

This is a little harder to read for me than just stubbing getPairedDevice to immediately call the passed in callback. ie, something like:
```
var stubGetPairedDevice =
  this.sinon.stub(BluetoothTransfer, 'getPairedDevice', function(getPairedDeviceComplete) {
    getPairedDeviceComplete();
  });
```