Update the base query in the UnifiedSearcherTest
Update integration helper to support auxiliary indexes
Configure page_traffic in the test environment

This renames "page-traffic" to "page_traffic", so that we can adopt the 
convention of appending "_test" to the index in the test environment.

This also adds configuration for "page_traffic_test", and changes 
Elasticsearch::Index to automatically infer the traffic index based on 
matching against the auxiliary indexes that are present.
Pre-fill popularity data in integration tests

This changes the multi-index and bulk-load integration tests so that, 
before we insert or update any documents in the search index, we seed 
the page_traffic index with mock popularity data for each URL.