Finalize the publish-pypi-package job

[gndrmnn]

We need to fix some small things in the publish-pypi-package job

• Use $HOME/venv instead of /tmp/venv as venv directory by default
• Make sure the upload-pypi upstream role has access to the variable containing the venv
• Use var pypi_twine_executable: "/tmp/venv/bin/python -m twine" for upload-pypi. Of course do not hard-code the path instead use the venv variable. (this obviously only works once upload-pypi knows the venv var).