Pass in harvest args to fasttest_acceptance, not the args array

Fixes this error from running `rake test_acceptance_lms["-v 3"]`:

    ./manage.py cms --settings acceptance harvest --traceback --debug-mode --tag -skip harvest_args -v 3
    You passed the path 'harvest_args', but it does not exist.

I introduced this accidentally while trying to speed up `fasttest_acceptance`.

@jzoldak