chore: supply UT for pkg/util and pkg/util/system

[ZiMengSheng]

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

Merging #374 (99ce220) into main (d763879) will increase coverage by 0.26%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #374      +/-   ##
==========================================
+ Coverage   66.28%   66.55%   +0.26%     
==========================================
  Files         116      116              
  Lines       11580    11580              
==========================================
+ Hits         7676     7707      +31     
+ Misses       3315     3283      -32     
- Partials      589      590       +1     

Flag	Coverage Δ
unittests	66.55% <ø> (+0.26%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/koordlet/runtimehooks/reconciler/reconciler.go	78.94% <0.00%> (-2.11%)	⬇️
pkg/util/system/cgroup.go	66.66% <0.00%> (+6.83%)	⬆️
pkg/util/utils.go	89.33% <0.00%> (+13.33%)	⬆️
pkg/util/resource.go	50.00% <0.00%> (+50.00%)	⬆️

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[jasonliu747]

Hi, thanks for your contribution. Please follow the instruction below to sign off your commit.

And BTW, I think you could also include TestMinInt64 and TestMaxInt64 like you did in the last PR.

[ZiMengSheng]

okay，I will add that.

[hormes]

/lgtm
/approve

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