add switch for log stdout

[chenzfp]

apache/dubbo-go#1960
fix:#490

[codecov-commenter]

Codecov Report

Merging #489 (66c75b2) into master (24e67a3) will increase coverage by 0.11%.
The diff coverage is 37.50%.

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
+ Coverage   51.00%   51.11%   +0.11%     
==========================================
  Files          25       25              
  Lines        2100     2107       +7     
==========================================
+ Hits         1071     1077       +6     
- Misses        940      941       +1     
  Partials       89       89              

Impacted Files	Coverage Δ
common/constant/client_config_options.go	87.83% <0.00%> (-3.72%)	⬇️
common/logger/logger.go	87.50% <33.33%> (-2.83%)	⬇️
clients/config_client/config_client.go	47.02% <100.00%> (+0.16%)	⬆️
clients/naming_client/naming_client.go	59.48% <100.00%> (+0.20%)	⬆️
clients/naming_client/beat_reactor.go	84.74% <0.00%> (+6.77%)	⬆️

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[binbin0325]

thanks for your contribution