tests: bootstrap 3 new nodes in full node replacement test

With tablets enabled, decommissioning a node from a 3-node cluster with
RF=3 fails because there is no available node to receive tablet replicas.
Bootstrap 3 replacement nodes instead of 2 so that each original node
can be decommissioned while sufficient replicas remain.

Author: sylwiaszunejko

tests/integration/standard/test_client_routes.py

@@ -1154,7 +1154,7 @@ def tearDownClass(cls):
     def test_should_survive_full_node_replacement_through_nlb(self):
         """
         1. Start with 3 nodes behind the NLB
-        2. Bootstrap 2 new nodes, add to NLB, update routes
+        2. Bootstrap 3 new nodes, add to NLB, update routes
         3. Decommission the original 3 nodes one-by-one, updating NLB/routes
         4. Verify the session survives with only new nodes
         """
@@ -1190,7 +1190,7 @@ def test_should_survive_full_node_replacement_through_nlb(self):
                          len(original_node_ids))
 
                 # ---- Stage 3: Bootstrap new nodes ----
-                new_node_ids = [max(original_node_ids) + 1, max(original_node_ids) + 2]
+                new_node_ids = [max(original_node_ids) + 1, max(original_node_ids) + 2, max(original_node_ids) + 3]
                 log.info("Stage 3: Adding nodes %s", new_node_ids)
                 ccm_cluster = get_cluster()