conn, util: make opentracing work again

[Defined2014]

What problem does this PR solve?

Issue Number: close #50508

Problem Summary: Caused by #40825, miss root span for opentracing tools.

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  Start a TiDB cluster as opentracing.enable not work after v7.1.0 #50508 said, and use JaegerUI to get trace info success.
  
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, tiancaiamao

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-18 07:53:26.991834517 +0000 UTC m=+428848.556132209: ☑️ agreed by hawkingrei.
• 2024-01-18 07:56:52.746232997 +0000 UTC m=+429054.310530701: ☑️ agreed by tiancaiamao.

[codecov]

Codecov Report

Merging #50551 (72e9140) into master (549a5d9) will decrease coverage by 14.6597%.
Report is 2 commits behind head on master.
The diff coverage is 0.0000%.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #50551         +/-   ##
=================================================
- Coverage   70.2609%   55.6013%   -14.6597%     
=================================================
  Files          1452       1563        +111     
  Lines        420451     587833     +167382     
=================================================
+ Hits         295413     326843      +31430     
- Misses       104700     238070     +133370     
- Partials      20338      22920       +2582     

Flag	Coverage Δ
integration	36.7890% <0.0000%> (?)
unit	70.1833% <0.0000%> (-0.0777%)	⬇️

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

Components	Coverage Δ
dumpling	54.0269% <ø> (ø)
parser	∅ <ø> (∅)
br	56.6524% <ø> (+6.1650%)	⬆️

[Defined2014]

/hold

[Defined2014]

/unhold

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #50556.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #50557.