QtIFW

Fix maintenance tool upgrade on OSX.

Before rename we need to delete a possible existing file,
otherwise it will fail and the installation is messed up.

Change-Id: I6ade434f828f11b38c00b52eabeb1c574557ec5a
Reviewed-by: Jonathan Courtois <jonathan.courtois@gmail.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>