[dubbo-1689]: Enhance the test coverage part-10 : dubbo-plugin module

[beiwei30]

What is the purpose of the change

issue#1689: Enhance the test coverage part-10 : dubbo-plugin module

Brief changelog

dubbo-plugin/dubbo-qos/src/main/java/org/apache/dubbo/qos/protocol/QosProtocolWrapper.java
dubbo-plugin/dubbo-qos/src/main/java/org/apache/dubbo/qos/server/Server.java
dubbo-plugin/dubbo-qos/src/test/java/org/apache/dubbo/qos/protocol/QosProtocolWrapperTest.java

Verifying this change

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a GITHUB_issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Format the pull request title like [Dubbo-XXX] Fix UnknownException when host config not exist #XXX. Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in test module.
• Run mvn clean install -DskipTests & mvn clean test-compile failsafe:integration-test to make sure unit-test and integration-test pass.
• If this contribution is large, please follow the Software Donation Guide.

[codecov-io]

Codecov Report

Merging #1982 into master will increase coverage by 0.2%.
The diff coverage is 37.5%.

@@            Coverage Diff             @@
##             master   #1982     +/-   ##
==========================================
+ Coverage      50.6%   50.8%   +0.2%     
- Complexity     4745    4763     +18     
==========================================
  Files           562     562             
  Lines         25213   25218      +5     
  Branches       4449    4449             
==========================================
+ Hits          12758   12811     +53     
+ Misses        10524   10470     -54     
- Partials       1931    1937      +6

Impacted Files	Coverage Δ	Complexity Δ
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	54.28% <20%> (+54.28%)	6 <0> (+6)	⬆️
.../main/java/org/apache/dubbo/qos/server/Server.java	72.09% <66.66%> (+72.09%)	10 <2> (+10)	⬆️
.../dubbo/remoting/transport/netty4/NettyChannel.java	60% <0%> (-5%)	21% <0%> (-1%)
...e/dubbo/remoting/transport/netty4/NettyServer.java	72.13% <0%> (-3.28%)	9% <0%> (-1%)
...he/dubbo/registry/multicast/MulticastRegistry.java	57.74% <0%> (+1.67%)	41% <0%> (+3%)	⬆️
...ubbo/rpc/protocol/dubbo/ChannelWrappedInvoker.java	50% <0%> (+8.33%)	3% <0%> (ø)	⬇️
...in/java/org/apache/dubbo/qos/server/DubboLogo.java	50% <0%> (+50%)	1% <0%> (+1%)	⬆️

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