[Testing] Reduce error verbosity of cleanup

[kylesayrs]

Purpose

• When tests fail, they often show the error that occurs during cleanup, rather than the error that caused the tests to fail

ERROR tests/llmcompressor/transformers/obcq/test_consecutive_runs.py::TestConsecutiveRunsSmall_0_commit::test_consecutive_runs_small - FileNotFoundError: [Errno 2] No such file or directory: './oneshot_output'

Changes

• Check if a directory exists before attempting to delete it during cleanup

[github-actions]

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Note: This is required to complete the testing suite, please only add the label once the PR is code complete and local testing has been performed.

[rahul-tuli]

Thoughts on using pathlib for these changes?