bugfix: fix ApplicationContext already closed problem when Seata server using ShutdownHook to destroy.

[Pinocchio2018]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

in develop version，when ShutdownHook doing destroyAll，an Exception happened because ApplicationContext is already closed

14:56:22.666 ERROR --- [             ShutdownHook] i.s.core.rpc.netty.NettyServerBootstrap  : shutdown execute error:org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@5a4c638d has been closed already
==>
java.lang.IllegalStateException: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@5a4c638d has been closed already
	at org.springframework.context.support.AbstractApplicationContext.assertBeanFactoryActive(AbstractApplicationContext.java:1093) ~[spring-context-5.2.14.RELEASE.jar:5.2.14.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1126) ~[spring-context-5.2.14.RELEASE.jar:5.2.14.RELEASE]
	at io.seata.spring.boot.autoconfigure.provider.SpringBootConfigurationProvider.get(SpringBootConfigurationProvider.java:100) ~[classes/:na]
	at io.seata.spring.boot.autoconfigure.provider.SpringBootConfigurationProvider.get(SpringBootConfigurationProvider.java:85) ~[classes/:na]
	at io.seata.spring.boot.autoconfigure.provider.SpringBootConfigurationProvider.access$200(SpringBootConfigurationProvider.java:46) ~[classes/:na]
	at io.seata.spring.boot.autoconfigure.provider.SpringBootConfigurationProvider$1.intercept(SpringBootConfigurationProvider.java:61) ~[classes/:na]
	at io.seata.config.FileConfiguration$$EnhancerByCGLIB$$862af1eb.getConfig(<generated>) ~[classes/:na]
	at io.seata.discovery.registry.nacos.NacosRegistryServiceImpl.getServiceName(NacosRegistryServiceImpl.java:214) ~[classes/:na]
	at io.seata.discovery.registry.nacos.NacosRegistryServiceImpl.unregister(NacosRegistryServiceImpl.java:92) ~[classes/:na]
	at io.seata.core.rpc.netty.NettyServerBootstrap.shutdown(NettyServerBootstrap.java:187) ~[classes/:na]
	at io.seata.core.rpc.netty.AbstractNettyRemotingServer.destroy(AbstractNettyRemotingServer.java:126) ~[classes/:na]
	at io.seata.core.rpc.ShutdownHook$DisposablePriorityWrapper.destroy(ShutdownHook.java:113) ~[classes/:na]
	at io.seata.core.rpc.ShutdownHook.destroyAll(ShutdownHook.java:82) ~[classes/:na]
	at io.seata.core.rpc.ShutdownHook.run(ShutdownHook.java:66) ~[classes/:na]
<==

Ⅱ. Does this pull request fix one issue?

fix #4028

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

I don't know how to write one in this problem.

Ⅳ. Describe how to verify it

1. checkout develop branch in idea，
2. using nacos as registry center
3. start ServerApplication in debug mode
4. stop the seata server, check if exceptions happens

Ⅴ. Special notes for reviews

[funky-eyes]

LGTM

[codecov-commenter]

Codecov Report

Merging #4032 (9993202) into develop (8fd705b) will increase coverage by 0.00%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##             develop    #4032   +/-   ##
==========================================
  Coverage      49.91%   49.91%           
- Complexity      3766     3767    +1     
==========================================
  Files            698      698           
  Lines          23498    23509   +11     
  Branches        2907     2910    +3     
==========================================
+ Hits           11729    11735    +6     
- Misses         10589    10593    +4     
- Partials        1180     1181    +1     

Impacted Files	Coverage Δ
...c/main/java/io/seata/server/ServerApplication.java	33.33% <ø> (ø)
...er/src/main/java/io/seata/server/ServerRunner.java	57.69% <50.00%> (-8.98%)	⬇️
server/src/main/java/io/seata/server/Server.java	75.00% <100.00%> (ø)
...o/seata/server/coordinator/DefaultCoordinator.java	55.37% <0.00%> (+0.53%)	⬆️

[slievrly]

LGTM