site.getsitepackages() doesn't respect --system-site-packages on python2

[freundTech]

Issue

site.getsitepackages() doesn't respect --system-site-packages being set on python2. System site-package paths are never included.
I came across this while working on #2105. In contrast to #2105 this is not specific to debian, which is why I am creating a separate issue for it.

python -m virtualenv --system-site-packages -ppython2 testenv
. testenv/bin/activate
python -c "import site; print(site.getsitepackages())"
['/home/adrian/Documents/dev/uni/bachelor/mypy/testenv/lib/python2.7/site-packages', '/home/adrian/Documents/dev/uni/bachelor/mypy/testenv/lib/site-python']

Environment

Provide at least:

• OS: Tested on both Ubuntu 18.04.3 LTS and Arch Linux
• pip list of the host python where virtualenv is installed:

Same as #2105

Output of the virtual environment creation

Make sure to run the creation with -vvv --with-traceback:
Same as #2105

[c0d3h4x0r]

This is still broken for my use case in virtualenv==20.4.6 w/ python 2.7.16 (at least on Windows).

site.getsitepackages() does not contain the system site packages locations when specifically called from within sitecustomize.py.

[c0d3h4x0r]

It appears to me that this ordering is wrong:

load_host_site() if global_site_package_enabled: add_global_site_package()

I'm guessing that add_global_site_package() really should be called before load_host_site().