DefaultApplicationProvider 在加载/META-INF/app.properties 文件时代码优化

[kangjiabang]

InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(APP_PROPERTIES_CLASSPATH); if (in == null) { in = DefaultApplicationProvider.class.getResourceAsStream(APP_PROPERTIES_CLASSPATH); }

DefaultApplicationProvider 在加载/META-INF/app.properties ,在使用contextClassLoader加载时，应该讲前缀"/"去除，否则加载到的结果为null，只能使用DefaultApplicationProvider.class.进行加载。

修改完成后，运行：
com.ctrip.framework.foundation.internals.provider.DefaultApplicationProviderTest#testLoadAppProperties ，结果OK

具体issue:
#2508

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@dce5116). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #2515   +/-   ##
=========================================
  Coverage          ?   50.19%           
  Complexity        ?     2046           
=========================================
  Files             ?      410           
  Lines             ?    12554           
  Branches          ?     1285           
=========================================
  Hits              ?     6301           
  Misses            ?     5806           
  Partials          ?      447

Impacted Files	Coverage Δ	Complexity Δ
...internals/provider/DefaultApplicationProvider.java	63.04% <100%> (ø)	11 <1> (?)

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[coveralls]

Coverage decreased (-0.008%) to 53.752% when pulling 0c53c98 on kangjiabang:master into dce5116 on ctripcorp:master.

[kangjiabang]

@JaredTan95 ,please review

[nobodyiam]

LGTM