parent/child: Explicitly disabled the query cache

It was already disabled, but during tests the test framework enabled the query cache by setting the static default query cache. The caching behaviour should be the same in production and in tests.

core/src/main/java/org/elasticsearch/index/query/HasChildQueryParser.java

@@ -258,6 +258,7 @@ public class HasChildQueryParser implements QueryParser {
             String joinField = ParentFieldMapper.joinField(parentType);
             IndexReader indexReader = searchContext.searcher().getIndexReader();
             IndexSearcher indexSearcher = new IndexSearcher(indexReader);
+            indexSearcher.setQueryCache(null);
             IndexParentChildFieldData indexParentChildFieldData = parentChildIndexFieldData.loadGlobal(indexReader);
             MultiDocValues.OrdinalMap ordinalMap = ParentChildIndexFieldData.getOrdinalMap(indexParentChildFieldData, parentType);
             return JoinUtil.createJoinQuery(joinField, innerQuery, toQuery, indexSearcher, scoreMode, ordinalMap, minChildren, maxChildren);