* Exporting Ipmi.Path to be set by config.

Currently "path" is not exported, giving this error when users try to
override the variable via telegraf.conf as per the sample config:

`field corresponding to `path' is not defined in `*ipmi_sensor.Ipmi'`

Exporting the variable solves the problem.

* Updating changelog.

added PDH_FMT_NOCAP100 format option

closes #2483

hopefully this will fix #2472

During issue #2215 it was highlighted that the current behavior where
rules without a comment are ignored is confusing for several users.

This commit improves the documentation and adds a NOTE to the sample
config to clarify the behavior for new users.

Tweak formatting of `LogicalDisk` counter array to have one entry per
line.

closes #1433

closes #2466

closes #2178

closes #2071

closes #2414

fixes #2380

closes #2390
closes #2404

fixes #2282

The docker engine-api package we use needs golang 1.7+, see:
https://github.com/docker/engine-api/pull/382#issuecomment-244512952

So telegraf won't compile without 1.7

closes #2339

Also, ensure pidfile perms are 644

closes #1516 
closes #1711 
closes #1721 
closes #1526 

* Procstat: don't cache PIDs

Changed the procstat input plugin to not cache PIDs. Solves #1636.
The logic of creating a process by pid was moved from `procstat.go` to
`spec_processor.go`.

* Procstat: go fmt

* procstat: modify changelog for #2206

closes #2244
closes #1547

this defer function was causing telegraf to call os.Exit(0) instead of
panicking when it was supposed to.

closes #2341

closes #2356