[BD-6] Fix check of virtualenv for virtualenv<20.0.0

[morenol]

Change the way to check if it is running in a virtualenv in order to be compatible with virtualenv>20.0.0 and virtualenv<20.0.0 (currently used in the platform)

I separated the change in three commits, so you can see that
1- in the first commit (using virtualenv<20.0.0) it is failing,
2- In the second commit, the changes fixed the problem for virtualenv<20.0.0
3- in the third commit we are using again virtualenv>20.0.0 and it is working

Reviewers

• @feanil

[openedx-webhooks]

Thanks for the pull request, @morenol! I've created OSPR-4822 to keep track of it in JIRA, where we prioritize reviews. Please note that it may take us up to several weeks or months to complete a review and merge your PR.

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[openedx-webhooks]

@morenol 🎉 Your pull request was merged!

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