Fix: After disconnection with ZK registry, cosumer can't listen to provider changes

[pantianying]

What this PR does:
fix #259 (comment)
Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-io]

Codecov Report

Merging #258 into develop will decrease coverage by 1.11%.
The diff coverage is 11.76%.

@@             Coverage Diff             @@
##           develop     #258      +/-   ##
===========================================
- Coverage    66.38%   65.26%   -1.12%     
===========================================
  Files          111      111              
  Lines         7038     7053      +15     
===========================================
- Hits          4672     4603      -69     
- Misses        1907     1993      +86     
+ Partials       459      457       -2

Impacted Files	Coverage Δ
registry/zookeeper/registry.go	55.79% <0%> (-2.99%)	⬇️
registry/zookeeper/listener.go	62.5% <100%> (+0.79%)	⬆️
cluster/cluster_impl/base_cluster_invoker.go	54.71% <0%> (-16.99%)	⬇️
protocol/dubbo/pool.go	57.86% <0%> (-15.74%)	⬇️
protocol/dubbo/listener.go	51.19% <0%> (-10.72%)	⬇️
protocol/dubbo/codec.go	76.47% <0%> (-5.89%)	⬇️
config_center/apollo/impl.go	84.41% <0%> (-2.6%)	⬇️
protocol/dubbo/readwriter.go	67.9% <0%> (-2.47%)	⬇️
remoting/zookeeper/listener.go	46.9% <0%> (-1.04%)	⬇️
registry/etcdv3/registry.go	50.5% <0%> (-1.02%)	⬇️
... and 1 more

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[vongosling]

@pantianying Do not use the topic style like "Fix: #259 #", Could you detail your fixing problem, getting more people to see what you're doing from the name and more people involved

[fangyincheng]

LGTM