fix issue 508

[nicktming]

What this PR does:

Which issue(s) this PR fixes:

Fixes #508

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Merging #510 (cd5ccb8) into develop (8ef6126) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop     #510      +/-   ##
===========================================
+ Coverage    54.72%   54.73%   +0.01%     
===========================================
  Files          664      664              
  Lines        77745    77746       +1     
===========================================
+ Hits         42544    42553       +9     
+ Misses       31562    31549      -13     
- Partials      3639     3644       +5     

Impacted Files	Coverage Δ
pixiu/pkg/client/dubbo/dubbo.go	21.60% <0.00%> (+3.59%)	⬆️
pkg/hbone/util.go	82.85% <0.00%> (-11.43%)	⬇️
pkg/envoy/admin.go	50.00% <0.00%> (-9.68%)	⬇️
pilot/pkg/networking/grpcgen/lds.go	90.51% <0.00%> (-1.73%)	⬇️
pkg/envoy/instance.go	76.27% <0.00%> (-1.70%)	⬇️
pkg/istio-agent/xds_proxy_delta.go	51.29% <0.00%> (-0.52%)	⬇️
security/pkg/credentialfetcher/fetcher.go	40.00% <0.00%> (ø)
.../pkg/serviceregistry/kube/controller/controller.go	72.68% <0.00%> (+0.15%)	⬆️
pilot/pkg/bootstrap/server.go	53.56% <0.00%> (+0.75%)	⬆️
pkg/istio-agent/xds_proxy.go	60.52% <0.00%> (+0.86%)	⬆️
... and 4 more

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[mark4z]

LGTM