util: add defaulting to blkio qos to improve robustness

[zqzten]

Ⅰ. Describe what this PR does

We've found a case that if we configure the resource qos config to ..."cgroupRoot":{"blkioQOS":{}}..., koordlet would crash due to a NPE panic in blkio reconcile.

This PR add the previously missing defaulting to blkio qos to solve this issue.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 66.31%. Comparing base (3963c04) to head (c91dd24).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2238      +/-   ##
==========================================
+ Coverage   66.28%   66.31%   +0.03%     
==========================================
  Files         453      453              
  Lines       53176    53214      +38     
==========================================
+ Hits        35248    35290      +42     
+ Misses      15390    15384       -6     
- Partials     2538     2540       +2     

Flag	Coverage Δ
unittests	66.31% <100.00%> (+0.03%)	⬆️

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[saintube]

/lgtm
/cc @zwzhang0107