Flaky transaction snippets

[tmatsuo]

https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/datastore/api/snippets.py#L655

I don't think get_multi guarantees that the order of the result is the same as the given keys. Please close if it does, but please fix this otherwise.

[theacodes]

This has been fixed.