Use a virtual environment for helix-scripts/

[dougbu]

Our Helix Python code is quite dependent on the Python packages installed along w/ the OS in most Linux distributions. In addition, cloud-init is a consistent Python-based package installed in most Linux systems in Azure. We do not currently separate ourselves from that default installation at all. Worse, even if we chose the newest python3 executable on a system (see #436), we end up sharing common package directories w/ the system.

The first step in #1363 is to move our Python use into a virtual environment. This will allow us to installer newer python3 executables pip and other Python packages based on our own requirements, not the stability requirements of most OS vendors.

Release Note Category

• Feature changes/additions
• Bug fixes
• Internal Infrastructure Improvements

Release Note Description

Moved our team's Python infrastructure into a venv, isolating us from the system. This should have minimal impact on customers because existing python3 executables and system-installed Python packages are not changing. However, if you use python3 in your pipelines and Helix jobs, some Python packages may be missing. Please let us know if you hit issues and are unable to use a venv (preferably in the Helix work item folder or build root).

[dougbu]

done in !35082 😁

[garath]

Looks like this broke at least one customer. See build 2329162. Teams FR converation here.