結論
$ wget -q -O - https://mackerel.io/file/script/setup-all-apt-v2.sh | MACKEREL_APIKEY='ここにAPIキー' sh $ sudo apt-get install mackerel-agent-plugins mackerel-check-plugins
$ wget -q -O - https://mackerel.io/file/script/setup-all-apt-v2.sh | MACKEREL_APIKEY='ここにAPIキー' sh $ sudo apt-get install mackerel-agent-plugins mackerel-check-plugins