Override cache settings during rb-site invocation.

Review Request #12457 — Created July 11, 2022 and submitted — Latest diff uploaded


Review Board


The change to move from MemcachedCache to PymemcacheCache broke
things when upgrading from a Python 2-based Review Board 3.0.x to Python
3-based 5.0 beta 1. The problem is that various code paths during
django.start() ended up triggering cache operations, and trying to set
up the old (pre-migrated) MemcachedCache would fail due to a missing
module. We migrate this setting during the upgrade process, but we never
got that far.

This change fixes rb-site to override any stored cache settings and just
use the local-memory cache for the duration of the command. This is
guaranteed to work regardless of what modules happen to be installed.

Ran rb-site upgrade on a site where the old environment used the
memcached package, and the new environment used the pymemcache