admindcli helper and test framework improvement (#9656)

[andy-fong]

Description

While working on the test for https://github.com/solo-io/solo-projects/issues/5455, found an issue with GetSingleListenerFromDynamicListeners() in admincli where it would crash if the config_dump returns an empty array.

Also, when running focused tests, the docker containers is left behind.

API changes

Code changes

• return error in GetSingleListenerFromDynamicListeners() if the config array is empty
• check docker container no longer exists before finishing AfterEach()

CI changes

Docs changes

Context

Interesting decisions

Testing steps

Notes for reviewers

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[solo-changelog-bot]

Issues linked to changelog:
#9656

[github-actions]

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