[feature request] On launch telegraf should create `telegraf` database if it doesn't already

[desa]

Currently the user has to create a telegraf database manually. The tool should do this for us.

[toddboom]

+1

[sparrc]

see commit c0cef8c

[alvaromorales]

Should the db name be configurable?

I've been running telegraf 1.4 and writing metrics to a database that's not named telegraf. If I upgrade to the next version, I'm going to have to migrate all my data to a new db. Happy to PR

[sparrc]

@alvaromorales yes, it should be, I'll fix that now