Ok, so I took a closer look at everything and I have two main concerns.

1. There's no test of the Write() function. If anything was broken in there, you probably wouldn't know, but at least the code is simple right now.
2. I looked closer at the Send() function from https://github.com/logzio/logzio-go/blob/master/logziosender.go, and I noticed that it has its own internal buffer, which competes with Telegraf's buffer, so essentially you've double buffered the output at twice the cost of memory for it. Not only this, but when the second logzio buffer is full, you drop metrics, meaning users can't control the buffer size from the config like other plugins anymore. The fix for this is to remove the use of logzio-go and just use a simple http connection to write the messages out. 90% of that package is buffering anyway, and you can just copy out the one http write function that you need.

Let me know what you think and if you have any questions.

I think you're good now. I kind of don't like that the connect function is used as an initializer (there's an Init() error function signature you can use for that), but you'd still need an empty Connect() function if you did that, so, I'll leave it up to you. Let me know when you're ready to merge.