qibuild: better support for QtCreator on mac

* use the .app instead of the real executable path
  (more robust)

* hard-code /Applications/Qt Creator.app

Change-Id: I4e588b648959fe7a168844205ffe0c035dd93482
Reviewed-on: http://gerrit.aldebaran.lan/21404
Tested-by: gerrit
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>