krb5_locator: always use port 88 for master KDC
    
    If the kpasswdinfo file exists and the found IP address includes a port
    number as well the master KDC lookup will use this port number which is
    most probably wrong. Better use the default port 88 always for master
    KDC lookups.
    
    This patch also updates the man page for the locator plugin which was
    quite outdated.
    
    Related to https://pagure.io/SSSD/sssd/issue/3958
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>