Retrieve user data from LDAP server.

def get_ldap_users(self):
        """Retrieve user data from LDAP server."""
        if (not self.conf_LDAP_SYNC_USER):
            return (None, None)
        user_keys = set(self.conf_LDAP_SYNC_USER_ATTRIBUTES.keys())
        user_keys.update(self.conf_LDAP_SYNC_USER_EXTRA_ATTRIBUTES)
        uri_users_server, users = self.ldap_search(self.conf_LDAP_SYNC_USER_FILTER, user_keys, self.conf_LDAP_SYNC_USER_INCREMENTAL, self.conf_LDAP_SYNC_USER_FILTER_INCREMENTAL)
        logger.debug("Retrieved %d users from %s LDAP server" % (len(users), uri_users_server))
        return (uri_users_server, users)