Fix rb-site (and prepare-dev.py) on Python 3 and Django 1.11.
Review Request #10681 — Created Sept. 6, 2019 and submitted
This addresses some string type consistency issues on Python 3 and
Django environment setup issues on Django 1.11, bringing us working
support for Django 1.11 on Python 3.
We also had to disable Django's built-in warnings checks during rb-site,
in order to not scare off users who think they have something that needs
to be fixed.
Installed and upgraded a site using Python 3 and Django 1.11.