Handle case when choose_best_option cannot find a candidate option

[Matouš Skála]

Currently, QTable.choose_best_option expects that the options returned by cloudomate contain the same options as present in QTable. What happens when the option selected by QTable cannot be found in an array returned by cloudomate_controller.options (e.g. the option was renamed, is not offered anymore, or cloudomate is broken)? Test and propose a fallback solution.