Update python virtual environment name

Change the repo python virtual environment name. This is a breaking
change. Repo synced after this commit need to rerun `m prereqs` or
`./scripts/install-prereqs -p scripts/python-requirements.txt -p
hw/opentitan-upstream/python-requirements.txt` or `mv cache/shodan-venv
cache/python-venv` to set up the python virtual environment.

Change-Id: Ice81a0e3f5ab8af3ddc991821765a25da0691964