allow multiple dashes in the components of server hostname
    
    Relax the check for valid hostname component by allowing multiple consecutive
    '-' or '/' characters int he middle of the label (the first/last character
    must still be alphanumeric or underscore). Also use verbose regex format to
    document its structure.
    
    https://fedorahosted.org/freeipa/ticket/4710
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>