tests: clean nodes from new pool in migration test

During normal startup procedure all Redpanda Service allocated nodes are
cleaned up before they are started. Added cleaning up the nodes from new
pool to make sure they are not using old data directory content.

Fixes: redpanda-data#13274

Signed-off-by: Michal Maslanka <michal@redpanda.com>

tests/rptest/tests/node_pool_migration_test.py

@@ -249,6 +249,11 @@ def test_migrating_redpanda_nodes_to_new_pool(self, balancing_mode):
 
         self.start_producer()
         self.start_consumer()
+        # clean new nodes to make sure they aren't using old data directory
+        self.redpanda.for_nodes(
+            new_pool,
+            lambda n: self.redpanda.clean_node(n,
+                                               preserve_current_install=True))
         # add new nodes to the cluster
         self.redpanda.for_nodes(
             new_pool,