zabbix

With buster the path to zabbix agent config files changed from
/etc/zabbix/zabbix_agentd.d/ to /etc/zabbix/zabbix_agent.conf.d/.
Also, the log directory changed from /var/log/zabbix/ to
/var/log/zabbix_agent, but after this change the agent logs to stdout
(journald) instead.