tests: use python3 to run http_api test to fix failed integration_tests (#5473)

[ti-chi-bot]

This is an automated cherry-pick of #5473

What problem does this PR solve?

Issue Number: close #5474

What is changed and how it works?

Our CI envs still default to python2 to run tests. http_api requires using requests which brings certifi. Actually certifi's recent releases doesn't support python2 any more.

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.2@2971ac3). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             release-5.2      #5478   +/-   ##
================================================
  Coverage               ?   57.9135%           
================================================
  Files                  ?        194           
  Lines                  ?      19631           
  Branches               ?          0           
================================================
  Hits                   ?      11369           
  Misses                 ?       7269           
  Partials               ?        993           

[zhangyangyu]

/run-all-tests

[Rustin170506]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 1c0b16b

[ti-chi-bot]

This pull request is closed because its related version has closed automatic cherry-picking.
If it's still needed, you can reopen it or just regenerate it using bot,
see:

https://prow.tidb.net/command-help#cherrypick
https://book.prow.tidb.net/#/plugins/cherrypicker