Usage guide test leaving BQ leftovers

[leahecole]

Every time the samples usage_guide test runs it leaves a leftover dataset in BigQuery. This test needs to be refactored to tear down the BigQuery dataset upon test completion.

python-logging/samples/snippets/usage_guide_test.py

Lines 51 to 58 in 330b53c

	def test_sink_bigquery():
	client = Client()
	to_delete = []
	usage_guide.sink_bigquery(client, to_delete)
	for item in to_delete:
	usage_guide._backoff_not_found(item.delete)

[leahecole]

Additionally, it seems like the test doesn't clean up the sink - a fixture should be added to delete the sink as well

EDIT: I think it does properly clean up sinks

[leahecole]

Instead of a fixture, I made a callback like the one used in the PubSub topic test