Finish Writing Namespace Tests

[srilman]

We should add more Python tests for namespace operations for the failure cases. We don't need to fix the test cases right now, but at least implement the tests. If the tests are currently failing, we can skip it in pytest. Some situations to test for:

• List namespaces, parent doesn't exist
• Create namespace,
• Create namespace, already exists
• Create namespace, parent namespace doesn't exist
• Load namespace, doesn't exist
• Drop namespace, doesn't exist
• Drop namespace, parent doesn't exist
• Update namespace properties, attempt to delete and update same key
• Update namespace properties, delete or update same key twice