issue#4314: ZookeeperDynamicConfiguration will be busy wait if zk is unavailable

[beiwei30]

What is the purpose of the change

fix #4134 and #4125

Brief changelog

dubbo-configcenter/dubbo-configcenter-zookeeper/src/main/java/org/apache/dubbo/configcenter/support/zookeeper/ZookeeperDynamicConfiguration.java
dubbo-remoting/dubbo-remoting-zookeeper/src/main/java/org/apache/dubbo/remoting/zookeeper/curator/CuratorZookeeperClient.java

Verifying this change

XXXXX

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

• Make sure there is a GITHUB_issue field 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 sample in dubbo samples project.
• Run mvn clean install -DskipTests=false & 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 #4582 into master will increase coverage by 0.04%.
The diff coverage is 60%.

@@             Coverage Diff              @@
##             master    #4582      +/-   ##
============================================
+ Coverage     63.29%   63.33%   +0.04%     
- Complexity      448      450       +2     
============================================
  Files           770      770              
  Lines         33008    33015       +7     
  Branches       5216     5217       +1     
============================================
+ Hits          20891    20911      +20     
+ Misses         9714     9704      -10     
+ Partials       2403     2400       -3

Impacted Files	Coverage Δ	Complexity Δ
...ting/zookeeper/curator/CuratorZookeeperClient.java	62.89% <100%> (ø)	0 <0> (ø)	⬇️
...pport/zookeeper/ZookeeperDynamicConfiguration.java	78.57% <50%> (-5.43%)	0 <0> (ø)
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	69.23% <0%> (-12.83%)	0% <0%> (ø)
...g/apache/dubbo/registry/consul/ConsulRegistry.java	59.6% <0%> (-0.67%)	27% <0%> (ø)
.../java/org/apache/dubbo/config/ReferenceConfig.java	59.48% <0%> (-0.37%)	0% <0%> (ø)
...g/context/annotation/DubboConfigConfiguration.java	66.66% <0%> (ø)	0% <0%> (ø)	⬇️
...pache/dubbo/registry/support/AbstractRegistry.java	81.6% <0%> (+0.38%)	0% <0%> (ø)	⬇️
...src/main/java/org/apache/dubbo/common/Version.java	62.62% <0%> (+1.57%)	0% <0%> (ø)	⬇️
...exchange/support/header/HeaderExchangeHandler.java	67.21% <0%> (+2.45%)	0% <0%> (ø)	⬇️
...bo/rpc/cluster/support/FailbackClusterInvoker.java	70.49% <0%> (+3.27%)	0% <0%> (ø)	⬇️
... and 7 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 05e44db...93f9cb2. Read the comment docs.

[tswstarplanet]

Should we add a flag to CuratorZookeeperClient to indicate if the INITIAL connection is established when we use ZookeeperRegistry ? If we don't check this, it will hang the main thread if the connection can not be established.

[cvictory]

LGTM