Fix zookeeper registry get wrong provider list. (#166)

[JervyShi]

Result:

Fixes #166

[codecov-io]

Codecov Report

Merging #174 into master will increase coverage by 0.26%.
The diff coverage is 74.5%.

@@             Coverage Diff              @@
##             master     #174      +/-   ##
============================================
+ Coverage     70.99%   71.26%   +0.26%     
  Complexity      955      955              
============================================
  Files           341      341              
  Lines         14196    14210      +14     
  Branches       2281     2286       +5     
============================================
+ Hits          10079    10127      +48     
+ Misses         2939     2891      -48     
- Partials       1178     1192      +14

Impacted Files	Coverage Δ	Complexity Δ
.../java/com/alipay/sofa/rpc/common/RpcConstants.java	100% <ø> (ø)	0 <0> (ø)	⬇️
...ipay/sofa/rpc/client/SingleGroupAddressHolder.java	98.21% <100%> (+0.1%)	0 <0> (ø)	⬇️
...alipay/sofa/rpc/registry/zk/ZookeeperRegistry.java	59.37% <50%> (+2.28%)	0 <0> (ø)	⬇️
...ofa/rpc/registry/zk/ZookeeperProviderObserver.java	70.17% <71.42%> (+1.65%)	0 <0> (ø)	⬇️
.../sofa/rpc/registry/zk/ZookeeperRegistryHelper.java	76.42% <73.52%> (+9.26%)	0 <0> (ø)	⬇️
...pay/sofa/rpc/transport/ClientTransportFactory.java	73.84% <0%> (-4.62%)	0% <0%> (ø)
.../main/java/com/alipay/sofa/rpc/tracer/Tracers.java	39.74% <0%> (-2.57%)	0% <0%> (ø)
...n/java/com/alipay/sofa/rpc/common/SofaConfigs.java	83.92% <0%> (-1.79%)	0% <0%> (ø)
...y/sofa/rpc/bootstrap/DefaultProviderBootstrap.java	66.49% <0%> (+2.53%)	0% <0%> (ø)	⬇️
... and 3 more

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[ujjboy]

No need to add this method because I add TestUtils.java at #180 contains this method. Just use TestUtils.delayGet() instead of it.

[JervyShi]

OK, I have fixed it.