Don't create user when USER_LOGIN is false, but for KDE install
    
    Summary:
    For some reason, we have `USER_LOGIN` set to 'false' for the KDE
    package set install test. I really don't know / remember why
    that would be; I'd think we should create a user and log in as
    that user to make sure it works properly when installing KDE
    from the traditional installer. It's not strictly part of the
    package set test, true, but still, seems worth doing.
    
    Also, when `USER_LOGIN` is set to 'false' and the installer runs,
    we create a user called 'false'. This doesn't seem like what we
    wanted, so let's not do that. I dunno if there are any other
    cases besides the KDE one that this commit changes, but still.
    
    Test Plan:
    Run the full test suite and look for weirdness, check
    KDE package set test works as intended (now creates a user called
    'test' and logs in as that user).
    
    Reviewers: jsedlak, jskladan
    
    Reviewed By: jsedlak
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qa.fedoraproject.org/D1182