Add MQTT output.

[shirou]

Add output which sends metrics to MQTT server.

The topic format is

<topic_prefix>/host/<hostname>/<pluginname>/<metric_name>
ex: prefix/host/web1.example.com/mem/available

hostname in a topic is specified in the outputs.mqtt config section, not agent Because I could not found how to inherit hostname value from agant.

[sparrc]

@shirou you should not have to manually update Godeps.json, try doing this:

$ go get github.com/tools/godep
$ godep save ./...

[sparrc]

@shirou thank you for the contribution! 👍 You shouldn't need to inherit the hostname tag, the agent should add that tag automatically in addition to the ones you add within this plugin

[shirou]

@sparrc Thank you for the comments. I type

godep restore
godep save ./...

Then, the other packages are also updated. If I made a mistake, I will revert it.

And, Thank you for the suggestion about hostname. I removed the settings in the MQTT section.

[sparrc]

Thanks @shirou! There was one problem with the Godep.json file. It was trying to manage the telegraf repo itself as a dependency. I'm not sure how that happened but I rebased your changes and removed that. Thanks again!

[sparrc]

@shirou don't forget to sign up for Hacktoberfest! https://hacktoberfest.digitalocean.com/, between this and gopsutil you should be able to get a free t-shirt ;-D