desktop_login: correct ownership of home dir after touching it
    
    Here we are creating ~/.config for a newly-created user with root
    ownership. We can't leave it that way, as commands run as the
    user account won't be able to change it, as they should be able
    to. So we need to change the ownership (and, just in case, fix
    SELinux contexts) afterwards.
    
    This was the real source of the problem we were seeing (the test
    failing early due to the gsettings command which should turn the
    screen background black failing).
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>