pyflakes warns about various errors, addressed here. For cls_cluster.py,
remove (unknown) sys.exit and replace through Exception, as sys.exit()
has the unwanted effect that the CI script would stop.  Instead, raise
an Exception that would show the problem in the HTML, and ensures that
the script runs until the end.

These are the warnings flagged by pyflakes.

    cls_cluster.py:297:4: undefined name 'sys'

    cls_containerize.py:39:1: 'subprocess' imported but unused
    cls_containerize.py:41:1: 'threading' imported but unused
    cls_containerize.py:43:1: 'multiprocessing.Process' imported but unused
    cls_containerize.py:43:1: 'multiprocessing.Lock' imported but unused
    cls_containerize.py:43:1: 'multiprocessing.SimpleQueue' imported but unused
    cls_containerize.py:49:1: 'cls_cluster as OC' imported but unused
    cls_containerize.py:50:1: redefinition of unused 'cls_cmd' from line 42

    cls_module.py:28:1: 'os' imported but unused
    cls_module...