Fix building of creator on Linux

Make sure that rpath's are sane. We used to rely on LD_LIBRARY_PATH,
but that doesn't work if the rpath recorded actually exists locally.

Change-Id: I43901ba196347c94fd5c4e86e54a7c994f394c65
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>