ACR Updates to fix failing tests

[annelo-msft]

Updates to fix failing nightly live tests.

• The multi-architecture images we were pulling from DockerHub added new architectures. Because of this, I learned I had my greater than or equals to operator in the wrong direction :-/
• Modifying the same resources at the same time from tests on different platforms was causing intermittent failures. I've updated all the tests that modify or delete an artifact to create a new independent artifact at the beginning of the test and clean it up at the end.

Fixes #21236

[christothes]

nit: If a SubString ends up being needed, it'd be better to do that before replacing values.

[annelo-msft]

Closing, given this approach doesn't work well with test recordings.