client: remote var `leader` which is the same as `forwardedHost`

[CabinfeverB]

What problem does this PR solve?

Issue Number: ref #4399

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot[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.

[codecov[bot]]

Codecov Report

Merging #7965 (2e68de2) into master (955d30a) will increase coverage by 0.05%. Report is 77 commits behind head on master. The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7965      +/-   ##
==========================================
+ Coverage   73.48%   73.54%   +0.05%     
==========================================
  Files         436      436              
  Lines       48376    48375       -1     
==========================================
+ Hits        35550    35576      +26     
+ Misses       9768     9743      -25     
+ Partials     3058     3056       -2     

Flag	Coverage Δ
unittests	73.54% <100.00%> (+0.05%)	:arrow_up:

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

[ti-chi-bot[bot]]

PR needs rebase.

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.