Error when grid parameter is not specified and/or when --execute-only flag is set

If there is no grid parameter given, the experiment would error with "TypeError: can only join an iterable" in bob/bio/base/tools/command_line.py, line 160 If --execute-only parameter is given, the experiment would error with: AttributeError: 'str' object has no attribute 'skip_extractor_training' in bob/bio/base/tools/command_line.py, line 274