test: add retries to flaky datalab-migration test

[kweinmeister]

Wraps the existing test with the Google API Core Retry decorator. The Retry defaults looked fine, so I didn't override any parameters.

Fixes #8331.

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• bigquery/datalab-migration/samples_test.py:276, tag bigquery_migration_datalab_load_table_from_dataframe
• bigquery/datalab-migration/samples_test.py:286, tag bigquery_migration_datalab_load_table_from_dataframe

You are about to delete 2 region tags.

• bigquery/datalab-migration/samples_test.py:273, tag bigquery_migration_datalab_load_table_from_dataframe
• bigquery/datalab-migration/samples_test.py:283, tag bigquery_migration_datalab_load_table_from_dataframe

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[leahecole]

Interesting, I didn't know/maybe I forgot that api core had a built in exponential retry. In the authoring guide we recommend backoff. Not sure if other @GoogleCloudPlatform/python-samples-reviewers have feelings about this vs. backoff. If we do stick with this, consider using the if_exception_type parameter on the specific error we're having problems with just to reduce retries on errors that are "legit"

[kweinmeister]

Sounds good. Happy to make changes if needed.

BTW, I was thinking the same thing about the scope of errors. I saw that the default scope for exception types is is_transient_error, which includes common "flaky" scenarios (which we can narrow down if using this class is OK).

[nicain]

LGTM