Class loading conflicts when using PowerMock in ITcase.

Currently when no user jars exist, system classLoader will be used to load classes as default. However, if we use powerMock to create some ITCases, the framework will utilize JavassistMockClassLoader to load classes.  Forcing the use of the system classLoader can lead to class loading conflict issue.

Therefore we should use Thread.currentThread().getContextClassLoader() instead of 
ClassLoader.getSystemClassLoader() here.