Fix Coverity finding CID 323644: logically dead code path
The code to determine whether NetBIOS name was already set or need to be
set after deriving it from a domain or asking a user for an interactive
input, was refactored at some point to avoid retrieving the whole LDAP
entry. Instead, it was provided with the actual NetBIOS name retrieved.
As result, a part of the code got neglected and was never executed.
Fix this code and provide a test that tries to test predefined,
interactively provided and automatically derived NetBIOS name depending
on how the installer is being run.
We mock up the actual execution so that no access to LDAP or Samba is
needed.
Fixes: https://pagure.io/freeipa/issue/7753
Reviewed-By: Christian Heimes <cheimes@redhat.com>
