Fix rb-site (and prepare-dev.py) on Python 3 and Django 1.11.

Review Request #10681 — Created Sept. 6, 2019 and submitted — Latest diff uploaded

Information

Review Board
release-4.0.x
57a0d3a...

Reviewers

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.