C++ and C# clients - java tests - reuse unchanged classes

In order to reuse the Java Client tests for the C++ and C# clients some of the API is duplicated in the C++/C# clients repo.

Changes required:

• keep in the C++/C# only the java classes which require changes
• for the rest of the classes required by the tests fetch the java client jar from maven and add it in the classpath after the modified classes