Use abbreviated output for stestr run in CI

[mtreinish]

Summary

This commit updates how we use stestr in CI to enable abbreviated output instead of the full output. Our test suite has grown to the point that printing each individual test case as a new line when it completes will overflow the github actions line limit for CI job logs. This makes it very inconvenient to identify the cause of a failure when a test fails because unless it's in the tests that get displayed before github stops displaying it you have to download the full log file (which you can view in the browser still but without the highlighting or direct link support). stestr has a less verbose output mode where it prints a single character for each test. . if a test succeeds, F for failure, etc. Test failures are still printed in full as is the summary footer. It's just the output of tests as they execute which is different. While this doesn't give the same level of diagnostic detail that the full output normally does it will not exceed github's limit. As a small side benefit from the benchmarking I did many years ago stestr actually executes slightly faster in this mode because it doesn't have to write nearly as much to stdout.

Details and comments

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[jakelishman]

Do you want to update the tox config too, or leave that as-is?

[mtreinish]

I left it as-is for now I did start there though before pushing. Local terminals don't have the same line limit as GitHub and it's simple enough to do tox -epy -- --abbreviate if you want this output. We also don't set --slowest in the tox config.