[Testing] c++ suite and python interface

[miguelmaso]

Description Currently, there are two tests suites, c++ and Python, having different interfaces. In #9906 there is a draft for adding the c++ tests to the python interface. The transition is backward compatible, since it simply extends the python testing interface, but the cpp suite needs to be populated explicitly. The usage is very handy, eg:

python3 test_AppName.py -l cpp

There are some TODO's before merging #9906 (registering individual tests, verbosity, skipping if c++ tests are disabled), but I'd like to hear other opinions

@KratosMultiphysics/technical-committee , @KratosMultiphysics/implementation-committee

[loumalouomega]

For me OK