Fix ConfigChangeContentBuilder update item issue

[nobodyiam]

hibernate will persist every changes made to entities during the session, so in ConfigChangeContentBuilder case, we should clone the entity first to not trigger unnecessary writes to the db. Because we will update the dataChangeLastModifiedTime when build is called.

[codecov-io]

Codecov Report

Merging #934 into master will increase coverage by 0.05%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master     #934      +/-   ##
============================================
+ Coverage     46.74%   46.79%   +0.05%     
- Complexity     1539     1542       +3     
============================================
  Files           352      352              
  Lines          9717     9721       +4     
  Branches        963      964       +1     
============================================
+ Hits           4542     4549       +7     
+ Misses         4832     4830       -2     
+ Partials        343      342       -1

Impacted Files	Coverage Δ	Complexity Δ
...k/apollo/biz/utils/ConfigChangeContentBuilder.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../apollo/internals/RemoteConfigLongPollService.java	77.91% <0%> (+1.22%)	28% <0%> (+1%)	⬆️
...work/apollo/biz/message/DatabaseMessageSender.java	66.66% <0%> (+10.41%)	8% <0%> (+2%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 13eda7c...3fc83f1. Read the comment docs.

[coveralls]

Coverage increased (+0.04%) to 50.314% when pulling 3fc83f1 on nobodyiam:fix-ConfigChangeContentBuilder-item into 13eda7c on ctripcorp:master.