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.