add influx key and repository

[bsmeding]

Add Influx repository and key for Apt to get telegraf package

[nervo]

Thanks for your pull request, but according to what is mentioned in the README.md pull requests must be send to the main Ansible Role repository :)

In this pull request we've just made, we add some more precise details about using apt role to reach the same goal: manala/ansible-roles#557

[bsmeding]

sorry to pull to the wrong repo, had read about it but forgot when fixing the Influx key and repo.

And for the second 'fix' is i can imagine that when using all the roles in a framework you can use a seperate role for adding the key, but for users who only want to install the telegraf role like me I dont really need (and want) to use seperate roles (and to check/update and maintain versions from them) for litte changes or additions, I want to have roles that work fully standalone for theire job.

[nervo]

This is perfectly understandable, but it goes against our philosophy of a role doing one thing, and doing it well :)