[TEST] MLT Rest test needs a mapping since we randomized number of nodes/shards

rest-api-spec/test/mlt/10_basic.yaml

@@ -7,6 +7,13 @@
          settings:
            index:
              number_of_replicas: 0
+         mappings:
+           test:
+             properties:
+               foo:
+                 type : "string"
+               title:
+                 type : "string"
 
   - do:
       index: