virtualenv exclude pre-installed by default

The list of packages included by default in a virtualenv is known and should be excluded by default when building.

If excluding modules, they are: setuptools, pip, easy_install, pkg_resources, and usually wheel if built with `virtualenv` instead of `venv`.

Start by locating the virtualenv build path that determines which pre-installed packages are included, then inspect any nearby tests. Verify the default exclusion behavior for setuptools, pip, easy_install, pkg_resources, and usually wheel when virtualenv rather than venv is used.

Written by the indexing model from the issue text.