Explicitly test for sysinfo files

[DL6ER]

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What does this PR aim to accomplish?:

Add an alternative implementation for the issue that should be solved in #295

How does this PR accomplish the above?:

Do not assume files exist and silence the error later but only use files we know existing.

Link documentation PRs if any are needed to support this PR:

N/A

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[DL6ER]

Rebased on latest development and cherry-picked @rdwebdesign's docker commit dbbc32c from #295

[yubiuser]

Rebased on current development. As DL6ER authored the PR and I added two commits someone else (@rdwebdesign ?) needs to approve.

[rdwebdesign]

One commit is mine too (41ce1c5)

Approved, anyway.

[yubiuser]

I know, but 1 is 1 less than two. So you are less "biased"