Don't show checkbox for Creator if root on Linux and Mac.

Task-number: QTCREATORBUG-9491

Change-Id: I977ab536b03d49f83ea9a8ba4a2f71563b53f57b
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>