pd_client: refine PD client codes

[JmPotato]

Signed-off-by: JmPotato ghzpotato@gmail.com

What problem does this PR solve?

Import macros from other crates with the use syntax.

What is changed and how it works?

rust-lang/rust#50911

Check List

Tests

• Unit test
• Integration test

Release note

• No release note.

[sre-bot]

No release note, Please follow https://github.com/pingcap/community/blob/master/contributors/release-note-checker.md

[nolouch]

lgtm

[BusyJay]

Cool, how about also cleaning other modules?

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• BusyJay
• nolouch

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[JmPotato]

/merge

[ti-chi-bot]

@JmPotato: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 14f80f4

[ti-chi-bot]

@JmPotato: Your PR has out-of-dated, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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 ti-community-infra/tichi repository.

[JmPotato]

Cool, how about also cleaning other modules?

Ok, I will take a look at other modules.