docker image: fluent.conf: use new environment vars for host and port
docker image: fluent.conf: use new environment vars for host and port

Signed-off-by: Eduardo Silva <81f705dc2ce1a61a2621e0e4b442a9474e1d0c70@treasure-data.com>

fluent/fluentd-kubernetes-daemonset,fluent/fluentd-kubernetes-daemonset,fluent/fluentd-kubernetes-daemonset