Better exceptions in python config
Better exceptions in python config

python/m5/config.py:
    Don't raise a new exception, just modify and re-raise the old one.

haowu4682/gem5,haowu4682/gem5,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,LingxiaoJIA/gem5,andrewfu0325/gem5-aladdin,haowu4682/gem5,andrewfu0325/gem5-aladdin,LingxiaoJIA/gem5,andrewfu0325/gem5-aladdin,haowu4682/gem5,LingxiaoJIA/gem5,andrewfu0325/gem5-aladdin,LingxiaoJIA/gem5,haowu4682/gem5,haowu4682/gem5,haowu4682/gem5,LingxiaoJIA/gem5,andrewfu0325/gem5-aladdin,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,LingxiaoJIA/gem5