Revert "Remove undefined variable in virtualenv_mod.py"

This reverts commit 8a7c40a63fb7c834922e26af4a20ae478f9ecd96.
Revert "virtualenv.managed: use "user" instead of "runas" for pip install"

This reverts commit 8099bda3059abbb76c5aba60b697bb0422581262.