Keep maven descriptor when building.

[ujjboy]

Motivation:

Keep maven descriptor file pom.properties and pom.xml when building.

[codecov-io]

Codecov Report

Merging #209 into 5.4 will decrease coverage by 0.04%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                5.4     #209      +/-   ##
============================================
- Coverage     71.27%   71.23%   -0.05%     
+ Complexity      959      958       -1     
============================================
  Files           341      341              
  Lines         14213    14213              
  Branches       2286     2286              
============================================
- Hits          10130    10124       -6     
- Misses         2891     2897       +6     
  Partials       1192     1192

Impacted Files	Coverage Δ	Complexity Δ
...y/sofa/rpc/bootstrap/DefaultProviderBootstrap.java	63.95% <0%> (-2.54%)	0% <0%> (ø)
...va/com/alipay/sofa/rpc/server/bolt/BoltServer.java	72.22% <0%> (-1.12%)	23% <0%> (-1%)

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