config-mod is capable of changing default SELinux user map order
and a default SELinux user. Validate the new config values to
prevent bogus default SELinux users to be assigned to IPA users.
https://fedorahosted.org/freeipa/ticket/2993
We need to compare two values and need to be aware of where those
values are coming from. They may come from options, setattr or
existing config. The format of that data is going to be different
depending on its source (always a list internally).
One may also set both at the same time so a standard validator cannot
be used because it lacks the context of the other value being set.
https://fedorahosted.org/freeipa/ticket/2938https://fedorahosted.org/freeipa/ticket/2940
The config plugin was adding together a list and a tuple, then
converting to a set.
Replace the operation with a set union.
Regression test included.
https://fedorahosted.org/freeipa/ticket/2706
