SMART plugin: measurement dropped when HDD under heavy use.

[marcv81]

Relevant telegraf.conf:

[[inputs.smart]]
  use_sudo = true
  attributes = true

System info:

Ubuntu 18.04 LTS

$ uname -a
Linux desktop 4.15.0-55-generic #60-Ubuntu SMP Tue Jul 2 18:22:20 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Telegraf version: latest master.

Steps to reproduce:

1. Enable the SMART input plugin.
2. Collect metrics.
3. Load the HDD: time sh -c "dd if=/dev/zero of=test bs=1M count=3k && sync" (should take around 30s on a modern HDD).

Expected behavior:

Telegraf captures SMART measurements for the supported block devices.

Actual behavior:

Telegraf does not capture any SMART measurements when the HDD is under load.

Additional info:

This is due to a hardcoded 5s timeout for smartctl. It is possible to verify that under those circumstances smartctl takes more than 5s even outside of Telegraf. Verified on 2 different computers with different HDDs.