Message Title

Spotted by org.hibernate.search.test.engine.worker.AsyncWorkerTest when run on Elasticsearch, it seems sone threads will attempt to use a LuceneHSQuery instead:

org.hibernate.search.exception.SearchException: HSEARCH000302: Cannot execute query 'name:emmanuel', as targeted entity type 'org.hibernate.search.test.engine.worker.Employee' is indexed through a non directory-based backend
	at org.hibernate.search.query.engine.impl.LuceneHSQuery.getIndexManagers(LuceneHSQuery.java:595)
	at org.hibernate.search.query.engine.impl.LuceneHSQuery.buildSearcher(LuceneHSQuery.java:401)
	at org.hibernate.search.query.engine.impl.LuceneHSQuery.buildSearcher(LuceneHSQuery.java:363)
	at org.hibernate.search.query.engine.impl.LuceneHSQuery.queryEntityInfos(LuceneHSQuery.java:126)
	at org.hibernate.search.query.hibernate.impl.FullTextQueryImpl.list(FullTextQueryImpl.java:202)
	at org.hibernate.search.test.engine.worker.WorkerTestCase$Work.run(WorkerTestCase.java:109)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)