Tests: avoid side effects from build_schema_wrong_backend test

Previously, this would pollute the global settings for the Whoosh
backend causing a failure if the Solr tests ran first. Now this
uses mock.patch which cleans up after itself automatically and
makes the intention of the code immediately obvious
AUTHORS: recognize Honza Kral's growing contributions

This was overdue based on significant contributions to the
ElasticSearch backend and modernizing the entire test suite