Test infrastructure redesign

• It is now possible to set a custom path to the logs directory which is helpful if different MBB runs should be stored in different output paths (--logs-dir).
• Further, the directory with the generated codes can now be specified (--gencodes) and is not hardcoded anymore.
• The logging infrastructure is revised: The full log output is still written to the logs directory, but the logging to stdout is now significantly reduced. If full output to stdout is still desired, there is now a --verbose option.
• There is now an option to specify a number of workers to ensure parallel execution (--nworkers). It uses the multiprocessing module of Python.
• The displacement problem in the MPI_Type_create_struct is now fixed.
• The logs directory is now "self-contained", i.e., the generation of output reports is not dependent on the gencodes directory anymore. All used source files are now also copied to the log directory. This allows to analyze different logs directory independently.