bqx: enable discuss@ authenticated queries for unified views

[stephen-soltesz]

The discuss@ authenticated bigquery-exporter queries verify that users with query privileges from membership in the discuss@ list preserve access to the bigquery tables published through measurement-lab project.

For the pass-through table views, this is a very simple and efficient test.

Today, the unified views are very inefficient. A simple, date limited query "date > 2 days ago" still scans the complete history, which scans ~3T of BQ data.

The bqx discuss@ queries should include queries to the unified views once they are more efficient to query.