Revise for new-style wiki auth
    
    Wiki auth was changed to use OpenID Connect (FAS auth) a while
    back. The credentials file and --username options became more
    or less obsolete at that time: wiki login ignores the creds file
    and the username options and goes via FAS. Let's update all the
    code and docs to reflect this and throw out some now-useless
    bits. For result reporting, we now just query the wiki for the
    username.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>