add a base EtcdModel to all dynamic created model

[Revolution1]

No description provided.

[codecov]

Codecov Report

Merging #79 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #79      +/-   ##
==========================================
+ Coverage   91.17%   91.18%   +0.01%     
==========================================
  Files          51       51              
  Lines        2786     2792       +6     
  Branches      286      286              
==========================================
+ Hits         2540     2546       +6     
  Misses        147      147              
  Partials       99       99

Impacted Files	Coverage Δ
etcd3/swagger_helper.py	77.86% <100%> (ø)	⬆️
etcd3/models.py	100% <100%> (ø)	⬆️
etcd3/stateful/lock.py	82.72% <100%> (+0.09%)	⬆️
etcd3/__init__.py	100% <100%> (ø)	⬆️

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