Modify the handling for ShowTablesMergedResult.

[tristaZero]

Fixes #954 .

Changes proposed in this pull request:

• Passthrough ShardingMeta info MergeEngine.
• Modify the handling for ShowTablesMergedResult.
• Modify some of test cases.

[codecov-io]

Codecov Report

Merging #960 into dev will increase coverage by 0.01%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##              dev     #960      +/-   ##
==========================================
+ Coverage   52.73%   52.75%   +0.01%     
==========================================
  Files         579      579              
  Lines       12120    12136      +16     
  Branches     1901     1905       +4     
==========================================
+ Hits         6392     6402      +10     
- Misses       5361     5364       +3     
- Partials      367      370       +3

Impacted Files	Coverage Δ
...proxy/backend/common/SQLPacketsBackendHandler.java	0% <0%> (ø)	⬆️
...shardingsphere/core/metadata/ShardingMetaData.java	2.22% <0%> (-0.28%)	⬇️
...backend/common/StatementExecuteBackendHandler.java	0% <0%> (ø)	⬆️
...proxy/backend/common/SQLExecuteBackendHandler.java	0% <0%> (ø)	⬆️
...shardingsphere/core/merger/MergeEngineFactory.java	100% <100%> (ø)	⬆️
...re/core/jdbc/core/statement/ShardingStatement.java	80.67% <100%> (+0.33%)	⬆️
...shardingsphere/core/merger/dal/DALMergeEngine.java	100% <100%> (ø)	⬆️
...jdbc/core/statement/ShardingPreparedStatement.java	83.68% <100%> (+0.23%)	⬆️
...e/core/merger/dal/show/ShowTablesMergedResult.java	87.5% <40%> (-8.93%)	⬇️
...OrchestrationMasterSlaveDataSourceFactoryBean.java	66.66% <0%> (-11.12%)	⬇️
... and 4 more

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