A variable reassignment in conf.py caused errors when we try to build
release versions of docs. Correct that by swapping the order of use
Since we support custom image prefixes, we should also support
imagePullSecrets since they are likely to be in a private registry.
This also updates some nearby documentation which was out of date.
We overrode the PXC resource values in order for functional tests
in minikube to work. Restore the defaults and set an override in
the functional tests.