refactor: Refactor of L0_backend_python and the env subtest

[nv-kmcgill53]

What does the PR do?

This PR refactors the L0_backend_python test to be able to incrementally run different parts of the test by using variables rather than having to comment out large sections of code.

Additionally this PR also refactors the env subtest to make use of configurable variables to run certain parts of the test on demand. This allows the L0_backend_python test to potentially be parallelized in the CI. This also turns silent failures into verbose failures, such as the Locale test in the env subtest currently failing even thought the CI says it's passing.

Checklist

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Commit Type:

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• build
• ci
• docs
• feat
• fix
• perf
• refactor
• revert
• style
• test

Related PRs:

triton-inference-server/python_backend#260
triton-inference-server/python_backend#384

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Background

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)

• closes GitHub issue: #xxx