Decouple testing framework API from Java test specific frameworks

[bartlomiej-laczkowski]

Recently I have played around with the new testing framework in Che 5.0.0-M9 (which currently supports JUnit and TestNG) and it would be nice if the core part could be decoupled from the implementation/support for the Java test frameworks. I think that this framework can be refactored to move its core part to Che core API to have it available to use like i.e. debugger API, that way all potential contributors (possibly me :-) would be able to easily add some new testing frameworks for other languages like i.e. PHP.

Che version: 5.0.0-M9
OS and version: Windows 10
Docker version: 1.12.3
Che install: Local build

Additional information:

Soon I will create a pull request with test framework refactoring proposal.