optimize: determine whether the server in the register is alive

[lj2018110133]

Ⅰ. Describe what this PR did

determine whether the server in the register is alive

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #3916 (ffaa5b2) into develop (65066d2) will increase coverage by 0.03%.
The diff coverage is 39.65%.

@@              Coverage Diff              @@
##             develop    #3916      +/-   ##
=============================================
+ Coverage      40.70%   40.74%   +0.03%     
- Complexity      3057     3073      +16     
=============================================
  Files            682      682              
  Lines          22925    23002      +77     
  Branches        2850     2867      +17     
=============================================
+ Hits            9332     9372      +40     
- Misses         12721    12753      +32     
- Partials         872      877       +5     

Impacted Files	Coverage Δ
...ta/core/rpc/netty/AbstractNettyRemotingClient.java	17.96% <0.00%> (ø)
...ta/discovery/registry/FileRegistryServiceImpl.java	0.00% <ø> (ø)
...a/io/seata/discovery/registry/RegistryService.java	0.00% <0.00%> (ø)
...eata/core/rpc/netty/NettyClientChannelManager.java	52.14% <38.77%> (-8.36%)	⬇️
...io/seata/core/rpc/netty/TmNettyRemotingClient.java	56.66% <66.66%> (+0.71%)	⬆️
...io/seata/core/rpc/netty/AbstractNettyRemoting.java	14.56% <0.00%> (-0.20%)	⬇️
...main/java/io/seata/common/util/ReflectionUtil.java	65.43% <0.00%> (+5.71%)	⬆️

[funky-eyes]

LGTM pr做个登记

[l81893521]

LGTM