Ref #2231 - Fix send-review-reminders and add it to daily cron
This fixes a syntax error and a Python 3 incompatibility, and adds
send-review-reminders to the daily cron script.
Important notes:
- I have not tested to what degree the existing reminders work as they
should, as that's out of scope. It does have tests.
- I can't assess whether the virtualenv activation works in the
production setup, and it may be obsolete as bin/daily also
activates the virtualenv.
- The same Python 3 incompatibility (execfile() no longer exists) seems
to exist in various other scripts.
- Legacy-Id: 16821
Note: SVN reference [16703] has been migrated to Git commit 296b126c70
d798196f5a