SERVER-40965 ensure noop index build request receives index already exists response in noop_writes_wait_for_write_concern.js

Author: benety

jstests/replsets/noop_writes_wait_for_write_concern.js

@@ -117,6 +117,7 @@
         confirmFunc: function(res) {
             assert.commandWorkedIgnoringWriteConcernErrors(res);
             assert.eq(res.numIndexesBefore, res.numIndexesAfter);
+            assert.eq(res.note, 'all indexes already exist');
         }
     });