[TEST] Fix failure in SearchFieldsTests.testUidBasedScriptFields.

Sorting fails on unmapped fields so the new propagation delay of the mappings
exposed this issue. I added explicit mappings as part of index creation to fix it.

src/test/java/org/elasticsearch/search/fields/SearchFieldsTests.java

@@ -185,7 +185,7 @@ public class SearchFieldsTests extends ElasticsearchIntegrationTest {
 
     @Test
     public void testUidBasedScriptFields() throws Exception {
-        createIndex("test");
+        prepareCreate("test").addMapping("type1", "num1", "type=long").execute().actionGet();
         ensureYellow();
 
         int numDocs = randomIntBetween(1, 30);