[Bugfix] update CI test image centos:6.7 to centos:7 to support run CI on arm

[Colvin-Y]

Ⅰ. Describe what this PR does

Update sts image in CI from centos:6.7 to centos:7 because version 7 is a multi-arch image but 6.7 not.

Ⅱ. Does this pull request fix one issue?

Fix issue #1616

Ⅲ. Describe how to verify it

All github CI should pass, and also this case can run on arm machine.

Ⅳ. Special notes for reviews

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.01%. Comparing base (0d0031a) to head (29c8290).
Report is 34 commits behind head on master.

❗ Current head 29c8290 differs from pull request most recent head 8a8384c. Consider uploading reports for the commit 8a8384c to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1623      +/-   ##
==========================================
+ Coverage   47.91%   49.01%   +1.09%     
==========================================
  Files         162      180      +18     
  Lines       23491    18803    -4688     
==========================================
- Hits        11256     9216    -2040     
+ Misses      11014     8375    -2639     
+ Partials     1221     1212       -9     

Flag	Coverage Δ
unittests	49.01% <ø> (+1.09%)	⬆️

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[furykerry]

/lgtm

[furykerry]

/approve

[kruise-bot]

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