[receiver/hostmetrics] Filesystem scraper doesn't respect env var when set

[atoulme]

Component(s)

No response

What happened?

When setting the environment variable HOST_PROC_MOUNTINFO, the filesystem scraper will read mount points from the proper location, but will still apply the root_path prefix to each mount point to read its information.

Instead, when the env var HOST_PROC_MOUNTINFO is set, we should not prefix the mount point with the root_path prefix.

Collector version

v0.108.0

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

No response

Log output

No response

Additional context

No response

[github-actions]

Pinging code owners:

• receiver/hostmetrics: @dmitryax @braydonk

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[rogercoll]

Is there any documentation about the HOST_PROC_MOUNTINFO env variable? I couldn't find any in the scraper's README https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/receiver/hostmetricsreceiver/internal/scraper/filesystemscraper/documentation.md but on the internal gopsutil package

Should we create a followup documentation issue?

[atoulme]

I have opened shirou/gopsutil#1707 to make this env var official in gopsutil. Once merged and adopted, we can document in the scraper.