smart: Gather S.M.A.R.T. information from storage devices

[rickard-von-essen]

This adds a new input plugin which uses the smartctl utility from the
smartmontools package to gather metrics from S.M.A.R.T. storage devices.

Signed-off-by: Rickard von Essen rickard.von.essen@gmail.com

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)

[rickard-von-essen]

I'll do some verification of this and come back when I think it's tested.

[sparrc]

@rickard-von-essen there is already a PR for this feature: #2319

feel free to re-open if your PR adds any additional functionality and you think we should use yours instead.

[rickard-von-essen]

Damn, #2319 must have been opened just after I started. I'll review and test that and comment there.

[rickard-von-essen]

@sparrc I think we should reopen this and compare the basic structure of the code with #2319.

[rickard-von-essen]

TODO:

• Properly handle exit codes
• Run gathering of metrics concurrently
• Split metrics into smart_device and smart_attribute.
• Handle versions 5.41, 5.42, 5.43, 6.[0-6]
• Update README.md, versions limitations (5.41, 5.42 + nocheck), new format, sudo

[rickard-von-essen]

EDIT: opened a new PR, see #2449

@sparrc I think we should reopen this (only collaborators/owners can do that).

I have updated this with more documentation, concurrent metrics gathering, different metrics structure, verified against version 5.41, 5.42, 5.43, 6.0, 6.1, 6.2, 6.3, 6.4, and 6.5.

@sebito91 It would be awesome if you would help testing this by testing the performance on your 96-disk system and verify that this would also cover your use case.