Fix graceful shutdown notify failure

[lilai23]

What type of PR is this?

Bug

What this PR does / why we need it?

When one instance of provider is going to be shutdown，send requests continuously to it. Sometimes we will get 500 response code. So this pr manages to make sure the notification to consumer is send correctly.

Which issue(s) this PR fixes？

Fixes #1589

Does this PR introduce a user-facing change?

No

Checklist

• Make sure there is a GitHub_issue related with this PR before you start working on it.
• Make sure you have squashed your change to one single commit.
• GitHub Actions works fine in this PR.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 7 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
...ermant/registry/service/impl/GraceServiceImpl.java	44.44%	5 Missing ⚠️
...n/java/io/sermant/registry/config/GraceConfig.java	50.00%	2 Missing ⚠️

Flag	Coverage Δ	Complexity Δ
unittests	42.97% <50.00%> (-0.02%)	182.00 <1.00> (+1.00)	⬇️

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

Files	Coverage Δ	Complexity Δ
...sermant/registry/entity/GraceShutdownBehavior.java	80.95% <100.00%> (+0.95%)	0.00 <0.00> (ø)
...n/java/io/sermant/registry/config/GraceConfig.java	57.89% <50.00%> (-0.35%)	29.00 <1.00> (+1.00)	⬇️
...ermant/registry/service/impl/GraceServiceImpl.java	66.66% <44.44%> (-8.34%)	0.00 <0.00> (ø)

... and 1 file with indirect coverage changes