added test clean up and customization

[dpatel-ops]

• add dynamo rest in conftest
• add common functions in utils to get test data
• allow user to pass custom model list, model dir, backend using env variables

[github-actions]

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[sducouedic]

I think it is ok to merge this PR as it is, but it is worth trying this suggestion in the future: IBM/vllm#77 (review)

[dpatel-ops]

Thanks @sducouedic, Agree, will try that in next pass and create a new PR once fixtures are working