Fix CGroupsV2 test

[mgencur]

The tests sometimes fail with CGroups V2:

  === CONT  TestShouldHaveCgroupReadOnly
    cgroup_test.go:155: Error getting cgroup information: strconv.Atoi: parsing "max": invalid syntax 

  === CONT  TestMustHaveCgroupConfigured
    cgroup_test.go:90: using cgroupv2
    cgroup_test.go:120: /sys/fs/cgroup/cpu.max = 100000, want: 1000
    cgroup_test.go:120: /sys/fs/cgroup/cpu.weight = 5, want: 128 

Proposed Changes

• Store CGroups information as strings (e.g. cgroup/cpu.max or cgroup/memory.max can be a string or have multiple values)
• Compute cpu.max correctly for CGroups V2

Release Note

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.01% 🎉

Comparison is base (a8a8be2) 86.13% compared to head (045dfa4) 86.15%.
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14355      +/-   ##
==========================================
+ Coverage   86.13%   86.15%   +0.01%     
==========================================
  Files         196      196              
  Lines       14781    14787       +6     
==========================================
+ Hits        12732    12739       +7     
- Misses       1742     1743       +1     
+ Partials      307      305       -2     

see 6 files with indirect coverage changes

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[dprotaso]

/assign @nak3

[nak3]

Thank you so much!
I realized that why previous PR passed the CI on upstream. We need to update ubuntu-20.04 to ubustu-latest which uses cgroup v2 in test step. (I updated build step only).

https://github.com/mgencur/serving-1/blob/cgroups_v2_fix/.github/workflows/kind-e2e.yaml#L85

Could you update it to ubuntu-latest?

[mgencur]

Could you update it to ubuntu-latest?

@nak3 Thanks for the pointer. Updated.

[nak3]

/lgtm
/approve

[knative-prow]

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