Reuse the same coordinator instance. resolve #924

[kezhenxu94]

Ⅰ. Describe what this PR did

Reuse the same coordinator instance

Ⅱ. Does this pull request fix one issue?

fixes #924

Ⅲ. Why don't you add test cases (unit test/integration test)?

did not change logic

Ⅳ. Describe how to verify it

CI passed

Ⅴ. Special notes for reviews

null

[codecov-io]

Codecov Report

Merging #925 into develop will decrease coverage by <.01%.
The diff coverage is 0%.

@@              Coverage Diff              @@
##             develop     #925      +/-   ##
=============================================
- Coverage      37.73%   37.73%   -0.01%     
  Complexity      1033     1033              
=============================================
  Files            224      224              
  Lines           8795     8793       -2     
  Branches        1063     1062       -1     
=============================================
- Hits            3319     3318       -1     
  Misses          5082     5082              
+ Partials         394      393       -1

Impacted Files	Coverage Δ	Complexity Δ
server/src/main/java/io/seata/server/Server.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...eata/core/rpc/netty/AbstractRpcRemotingClient.java	17.22% <0%> (-0.48%)	7% <0%> (ø)

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[xingfudeshi]

Thanks.LGTM.