tests/node_ops: avoid interference betwen failure injections and ops

They can already be separated with a lock, but it's not sufficient.
We need certain delay between them.

tests/rptest/tests/random_node_operations_test.py

@@ -10,6 +10,7 @@
 import random
 import re
 import threading
+import time
 from rptest.clients.rpk import RpkTool
 from rptest.services.admin import Admin
 from rptest.tests.prealloc_nodes import PreallocNodesTest
@@ -463,7 +464,8 @@ def enable_write_caching_testing():
             self.redpanda,
             self.logger,
             lock,
-            progress_timeout=120 if enable_failures else 60)
+            progress_timeout=120 if enable_failures else 60,
+            wait_after_decommission=60 enable_failures else 0)
         for i, op in enumerate(
                 generate_random_workload(
                     available_nodes=self.active_node_idxs)):

tests/rptest/utils/node_operations.py

@@ -215,12 +215,14 @@ def __init__(self,
                  redpanda: RedpandaService,
                  logger,
                  lock: threading.Lock,
-                 progress_timeout=60):
+                 progress_timeout=60,
+                 wait_after_decommission=0):
         self.redpanda = redpanda
         self.logger = logger
         self.timeout = 360
         self.lock = lock
         self.progress_timeout = progress_timeout
+        self.wait_after_decommission = wait_after_decommission
 
     def node_id(self, idx):
         return self.redpanda.node_id(self.redpanda.get_node(idx),
@@ -257,6 +259,7 @@ def decommissioned():
                    node_removed(node_id),
                    timeout_sec=self.timeout,
                    backoff_sec=1)
+        time.sleep(wait_after_decommission)
 
     def get_statuses(self, node_to_query=None):
         admin = Admin(self.redpanda)