The final output directory was not being created since we got rid of tmpdir.mkdir(parents=True, exist_ok=False) in mapreduce.py, so I added a line to create it. However, it does seem like the tests are not working as intended because they would've caught that bug. I can either address it in this PR or in a separate PR. But otherwise, LGTM.
@jaredzh pointed out https://github.com/eecs485staff/madoop/pull/24#pullrequestreview-812647293