Fix addKeys operation in qt.510.android_qtcreator_settings

Don't remove the key when uninstalling, since other versions
might still use it. Also, handle when sdktool reports that
the key has already been set (4).

Change-Id: I5eeb5124b9ec20691d9a4c79ca92791ad232679d
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>