ApplyProductKeyOperation::performOperation should return correctly

The ApplyProductKeyOperation::performOperation should return false
whent the actual operation has failed.
Currently even if the operation fails and returns false the installer
will keep on installing without user interaction.

Change-Id: I68020f8200cebbc45bca164d66fb876e170f3721
Reviewed-by: Antti Kokko <antti.kokko@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>