Some refactoring after review

[fkorotkov]

Please check commit by commit messages and changes. Please let me know if you have any concerns.

[codecov]

Codecov Report

Merging #1 into master will increase coverage by 0.69%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master       #1      +/-   ##
==========================================
+ Coverage   86.91%   87.61%   +0.69%     
==========================================
  Files           3        3              
  Lines         107      113       +6     
==========================================
+ Hits           93       99       +6     
+ Misses          8        7       -1     
- Partials        6        7       +1     

Impacted Files	Coverage Δ
preprocessor/expander.go	89.47% <80.00%> (+3.03%)	⬆️
preprocessor/preprocessor.go	87.75% <90.00%> (-2.49%)	⬇️

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[edigaryev]

I've fixed a minor linter error to let the pipeline go (46a06ad) and found some useless code path from the original implementation while investigating the coverage drop (aaeffba). Hopefully you don't mind :)

[edigaryev]

It seems that Codecov check results are now being affected by an issue similar to kata-containers/tests#508.

Judging by the fact that this still isn't fixed since 2018 at the Codecov's side, I've disabled the check in 02bac8b.

Perhaps one day we should try Coveralls to see if it's any better.

[edigaryev]

Thanks for the submission, the changes are dope (especially the function closure) 👍