Scroll search should clear the scroll at the end (#1331)

lib/Helpers.js

@@ -104,13 +104,15 @@ class Helpers {
     }
 
     while (response.body.hits && response.body.hits.hits.length > 0) {
+      // scroll id is always present in the response, but it might
+      // change over time based on the number of shards
       scroll_id = response.body._scroll_id
       response.clear = clear
       addDocumentsGetter(response)
 
       yield response
 
-      if (!scroll_id || stop === true) {
+      if (stop === true) {
         break
       }
 
@@ -127,6 +129,10 @@ class Helpers {
         throw new ResponseError(response)
       }
     }
+
+    if (stop === false) {
+      await clear()
+    }
   }
 
   /**