CONFIG: add missing ldap attributes for validation
https://pagure.io/SSSD/sssd/issue/3961
This patch adds missing 'ldap_host_*' attributes for config validation.
Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>
(cherry picked from commit 85e363086fb7fd859c9b2eda408ec83addd79008)