sudo ldap provider: support autoconfiguration of hostnames
    
    https://fedorahosted.org/sssd/ticket/1420
    
    sudoHost attribute may contain hostname or fqdn of the machine.
    Sudo itself supports only one hostname and its fqdn - the one that
    is returned by gethostbyname().
    
    This patch implements autoconfiguration of hostname and fqdn if
    it has not been set manually by ldap_sudo_hostnames option.