Add -config-directory argument to Windows service

[cosmopetrich]

Fixes #1797

Telegraf will fail to start if given a -config-directory that doesn't exist. The arguments used by the service won't change unless Telegraf is run with -service install and -service uninstall, so breakage as a result of this change seems unlikely.

Required for all PRs:

• CHANGELOG.md updated (we recommend not updating this until the PR has been approved by a maintainer)
• Sign CLA (if not already signed)
• README.md updated (if adding a new plugin)

[sparrc]

you need to run go fmt ./... on your code

[cosmopetrich]

Sorry about that. Fixed.

[cosmopetrich]

It looks like scripts/build.py doesn't create the telegraf.d directory, so that won't be included in the Windows .zip file. On Linux, scripts/post-install.sh takes care of creating that directory.

Is that something we should worry about here, or should it be left up to users installing the service on Windows?

[sparrc]

can you modify build.py to make that directory?

[sparrc]

ping

[sparrc]

build.py update

[cosmopetrich]

Apologies @sparrc, I hadn't had a chance to revisit this yet.

It looks like it may have been superseded by #2330?

[cosmopetrich]

Ah, no, that doesn't set a default.

[danielnelson]

I added a bit of documentation around using the configuration directory in Windows as a service. a9afd2f

I don't think we should set a default value across the board, but if we add an installer in the future it could help setup a location and directory for this.