Resolve placeholder in datasource configuration

[errordaiwa]

Fixes #1011 .

Changes proposed in this pull request:

• fix an issue where placeholder like ${} in datasource configuration can't be resolved
• add integration test case for placeholder resolving

[codecov-io]

Codecov Report

Merging #1020 into dev will increase coverage by 0.04%.
The diff coverage is 92.3%.

@@            Coverage Diff             @@
##              dev    #1020      +/-   ##
==========================================
+ Coverage   54.93%   54.98%   +0.04%     
==========================================
  Files         630      630              
  Lines       12325    12349      +24     
  Branches     1972     1976       +4     
==========================================
+ Hits         6771     6790      +19     
- Misses       5142     5144       +2     
- Partials      412      415       +3

Impacted Files	Coverage Δ
...c/orchestration/spring/boot/util/PropertyUtil.java	53.84% <92.3%> (+16.8%)	⬆️
...dingsphere/jdbc/spring/boot/util/PropertyUtil.java	53.84% <92.3%> (+16.8%)	⬆️
...ngsphere/opentracing/sampling/SamplingService.java	88% <0%> (-12%)	⬇️
...OrchestrationMasterSlaveDataSourceFactoryBean.java	66.66% <0%> (-11.12%)	⬇️
.../internal/config/ConfigurationListenerManager.java	56.75% <0%> (+2.7%)	⬆️

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[terrymanu]

thank you for contribute code