Fix: zk lost event

[wenxuwan]

What this PR does:
try to fix #660

[fangyincheng]

LGTM

[codecov-commenter]

Codecov Report

Merging #692 into master will decrease coverage by 0.02%.
The diff coverage is 44.82%.

@@            Coverage Diff             @@
##           master     #692      +/-   ##
==========================================
- Coverage   63.88%   63.85%   -0.03%     
==========================================
  Files         236      236              
  Lines       12313    12332      +19     
==========================================
+ Hits         7866     7875       +9     
- Misses       3680     3690      +10     
  Partials      767      767              

Impacted Files	Coverage Δ
remoting/zookeeper/listener.go	47.19% <38.46%> (-0.79%)	⬇️
config/registry_config.go	79.31% <100.00%> (+0.36%)	⬆️
registry/zookeeper/registry.go	56.29% <100.00%> (+0.58%)	⬆️
cluster/cluster_impl/failback_cluster_invoker.go	78.02% <0.00%> (-2.20%)	⬇️
protocol/dubbo/client.go	67.87% <0.00%> (-1.22%)	⬇️
remoting/kubernetes/listener.go	52.83% <0.00%> (ø)
remoting/kubernetes/watch.go	80.73% <0.00%> (+1.83%)	⬆️
remoting/kubernetes/client.go	78.75% <0.00%> (+2.50%)	⬆️

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[gaoxinge]

LGTM