[3.0] improve unit test efficiency

[kylixs]

What is the purpose of the change

• Upgrade maven to 3.8.1
• Short shutdown wait time dubbo.service.shutdown.wait
• Netty4 support shutdown timeout

[codecov-commenter]

Codecov Report

Merging #8877 (c26bcbb) into 3.0 (9a0629c) will decrease coverage by 0.06%.
The diff coverage is 81.53%.

@@             Coverage Diff              @@
##                3.0    #8877      +/-   ##
============================================
- Coverage     63.87%   63.80%   -0.07%     
- Complexity      314      315       +1     
============================================
  Files          1169     1170       +1     
  Lines         49239    49375     +136     
  Branches       7366     7376      +10     
============================================
+ Hits          31450    31506      +56     
- Misses        14368    14428      +60     
- Partials       3421     3441      +20     

Impacted Files	Coverage Δ
...apache/dubbo/common/config/ConfigurationUtils.java	73.77% <ø> (ø)
...main/java/org/apache/dubbo/rpc/ProtocolServer.java	0.00% <ø> (ø)
...ache/dubbo/rpc/protocol/AbstractProxyProtocol.java	58.13% <50.00%> (-0.20%)	⬇️
...ubbo/rpc/protocol/rest/BaseRestProtocolServer.java	82.60% <50.00%> (-3.11%)	⬇️
...java/org/apache/dubbo/remoting/api/Connection.java	72.03% <62.96%> (+0.46%)	⬆️
...ache/dubbo/remoting/api/PortUnificationServer.java	82.85% <100.00%> (+1.31%)	⬆️
...e/dubbo/remoting/transport/netty4/NettyServer.java	75.71% <100.00%> (+1.86%)	⬆️
...rg/apache/dubbo/rpc/protocol/AbstractProtocol.java	79.48% <100.00%> (+2.34%)	⬆️
...apache/dubbo/rpc/protocol/dubbo/DubboProtocol.java	61.98% <100.00%> (+0.66%)	⬆️
.../dubbo/rpc/protocol/dubbo/DubboProtocolServer.java	64.28% <100.00%> (+5.95%)	⬆️
... and 36 more

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[chickenlj]

LGTM