Supports service discovery with Etcd

[xingfudeshi]

Ⅰ. Describe what this PR did

Supports service discovery with Etcd

Ⅱ. Does this pull request fix one issue?

fixes #812

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

i have done integration test.

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #869 into develop will decrease coverage by 0.5%.
The diff coverage is 0.76%.

@@              Coverage Diff              @@
##             develop     #869      +/-   ##
=============================================
- Coverage      38.29%   37.78%   -0.51%     
  Complexity      1033     1033              
=============================================
  Files            222      224       +2     
  Lines           8665     8795     +130     
  Branches        1051     1063      +12     
=============================================
+ Hits            3318     3323       +5     
- Misses          4953     5078     +125     
  Partials         394      394

Impacted Files	Coverage Δ	Complexity Δ
...discovery/registery/etcd/EtcdRegistryProvider.java	0% <0%> (ø)	0 <0> (?)
...covery/registery/etcd/EtcdRegistryServiceImpl.java	0% <0%> (ø)	0 <0> (?)
...java/io/seata/discovery/registry/RegistryType.java	38.46% <33.33%> (-0.67%)	2 <0> (ø)
...o/seata/server/coordinator/DefaultCoordinator.java	54.86% <0%> (+1.38%)	17% <0%> (ø)	⬇️
...ain/java/io/seata/core/rpc/netty/ShutdownHook.java	62.5% <0%> (+6.25%)	6% <0%> (ø)	⬇️

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[slievrly]

LGTM

[zhangthen]

+1