Raise SystemExit if breeze test specifies a directory that is also ignored

[topherinternational]

Followup to #41967 and parallel to #41991

My proposal is that we remove the behavior that detected an --ignore switch and removed the pytest directory arg, and instead fail out of the test call when this scenario is detected.

Pytest prioritizes the test arg over the ignore switch, so this code was inverting the way pytest expects to be used which creates complexity when reasoning about breeze and the CI test suites. Also, with #41991, we should be not calling these kinds of scenarios anyway, and raising an error will help us locate any straggler cases.

IOW, the command pytest tests/providers/alpha --ignore=tests/providers/alpha will run the tests in tests/providers/alpha (the ignore is ignored). Our change in #40037 attempted to override this behavior and prioritize the ignore switch; it is simpler to understand the system if we detect these scenarios upstream instead of force-fitting the reverse of how pytest wants to work.

This change refactors the _run_test function in the following ways:

• All arguments for docker down and docker run commands are built before any docker calls are made
• A check is made to see if any pytest directory arg is also specified in an --ignore=<dir> switch; if so, a system exit is initiated
• Some argument construction steps are moved into dedicated functions for readability and testability

Tests have been added to verify the exit functionality and also validate some of the collaborator calls. I didn't feel the need to test the entire control flow.

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[potiuk]

I am at the Airflow Summit - not sure if I will be able to take a look before my holidays after :(

[potiuk]

I am at the Airflow Summit - not sure if I will be able to take a look before my holidays after :(

[github-actions]

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