Plugin doesn't seem to honor env vars

[Aaron Sachs]

Dropping this in https://sensucommunity.slack.com/archives/C68LV5M9U/p1576173807165800 and also https://sensucommunity.slack.com/archives/C68LV5M9U/p1576082292124700. I thought that I'd tested this, but am now second-guessing myself on the changes in 36d6003

[Jef Spaleta]

So far my testing indicates envvars are working,.
But i'm releasing 3.0.0 now that has some changes to help here.

1.. better usage message
2.. a dryrun mode that can be used to help diagnose problems with envvar if they occur

[Jef Spaleta]

re-open if there's more info from using 3.0.0