Fix flaky test that tests lots of threads calling emit. Make sure tests shutdown the batch exporter.#4600

xrmx merged 6 commits intoopen-telemetry:mainopen-telemetry/opentelemetry-python:mainfrom

DylanRussell:fix_broken_test_and_shutdown_threadsDylanRussell/opentelemetry-python:fix_broken_test_and_shutdown_threadsCopy head branch name to clipboard