[YUNIKORN-2525] dispatcher.Stop() waits an extra second unnecessarily

[pbacsko]

What is this PR for?

Speed up dispatcher.Stop() which also makes unit tests run faster.

What type of PR is it?

• - Bug Fix
• - Improvement
• - Feature
• - Documentation
• - Hot Fix
• - Refactoring

Todos

• - Task

What is the Jira issue?

https://issues.apache.org/jira/browse/YUNIKORN-2525

How should this be tested?

Screenshots (if appropriate)

Questions:

• - The licenses files need update.
• - There is breaking changes for older versions.
• - It needs documentation.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 71.78%. Comparing base (8be3910) to head (f4c9f12).

Files	Patch %	Lines
pkg/dispatcher/dispatcher.go	76.92%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #811      +/-   ##
==========================================
- Coverage   71.79%   71.78%   -0.02%     
==========================================
  Files          43       43              
  Lines        6351     6358       +7     
==========================================
+ Hits         4560     4564       +4     
- Misses       1589     1592       +3     
  Partials      202      202              

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[chia7712]

overall +1 and one minor comment left.

[chenyulin0719]

+1 LGTM