Update Telegraf service parameters when Docker is updated to >= 1.12.

What must be done

Brave knight, you shall undo the evil done by commith monitoring/monitoring@7adc5e5b5e79170cea53672c8595baee47d971cd.

Id est, in roles/telegraf/tasks/install.yml change

docker_service_parameters: "--privileged --net=host"

to

docker_service_parameters: "--privileged --network host"