Comment 7 for bug 1260290

And if you want to set wsrep_provider_option in none_provider, you have to give all parameters.

The reason why I don't choose concatenation of parameters, although it's convenient for user to set, is because it would not allow you to clear wsrep_provider_option. And I think it's acceptable for user to give all parameters in none provider, because after all changing provider in runtime is rare case.