Create helper lightweight framework for testing MuranoPL

Nearly all MuranoPL tests need to load MuranoPL YAML classes, setup all DSL plumbing (setup class loader, executor, root context etc.), invoke MuranoPL members and test their behavior. This common pattern may be extracted into lightweight testing framework that provide test suits with customized class loader capable of loading sample YAML files from directory (next to python test file) and provide helpful syntax to quickly build Object Model, load it and invoke different methods