Refine the venv setup process. am: da7edd0aa6 am: ce9db403ca am: f6df9bb95a am: 7608794f93

Original change: https://googleplex-android-review.googlesource.com/c/platform/tools/test/openhst/+/12191405

Change-Id: Ia539096aeeb5b93fd79bd1960c5a7798f2de38e2