python bv vars py prefix

[cyrush]

Description

Resolves #19443

Type of change

• [ ] Bug fix~~
• [ ] New feature~~
• [ ] Documentation update~~
• [x] Other~~

build_visit change

How Has This Been Tested?

Needs to be tested as part of 3.4.2 release builds.

Reminders:

• Please follow the style guidelines of this project.
• Please perform a self-review of your code before submitting a PR and asking others to review it.
• Please assign reviewers (see VisIt's PR procedures for more information).

Checklist:

- [ ] I have commented my code where applicable. - [ ] I have updated the release notes. - [ ] I have made corresponding changes to the documentation. - [ ] I have added debugging support to my changes. - [ ] I have added tests that prove my fix is effective or that my feature works. - [ ] I have confirmed new and existing unit tests pass locally with my changes. - [ ] I have added new baselines for any new tests to the repo.

• [x] I have NOT made any changes to protocol or public interfaces in an RC branch.~~