Instead of having to manually stub packages that should not be
downloaded we instead automatically stub all packages (except a small
list of whitelisted ones). Tests can re-introduce the real package by
using the `realPkgs` module argument.
Before this change, the default config provided by this module wrote
an empty file to `$HOME/.config/avizo/config.ini`, which caused a
bunch of errors, as Avizo tries to read a 'group' from the ini file,
which fails.
This commit also adds associated test cases.
PR #3871