Fix sg cleanup: raise exception on last attemp

Related-PROD: PRODX-4003
Change-Id: I832dd8252635860a40b42a9f8c3f8de87f6ed845
diff --git a/tempest/lib/common/dynamic_creds.py b/tempest/lib/common/dynamic_creds.py
index 2cb0669..c1df32c 100644
--- a/tempest/lib/common/dynamic_creds.py
+++ b/tempest/lib/common/dynamic_creds.py
@@ -404,7 +404,8 @@
         secgroups_to_delete = resp_body['security_groups']
         for secgroup in secgroups_to_delete:
             # Workaround for PRODX-4003
-            for i in range(5):
+            attempts = 5
+            for i in range(attempts):
                 try:
                     nsg_client.delete_security_group(secgroup['id'])
                     break
@@ -415,8 +416,11 @@
                 except lib_exc.Conflict:
                     LOG.warning('Conflict with state of security group %s, '
                                 'id %s.', secgroup['name'], secgroup['id'])
-                    time.sleep(1)
-                    continue
+                    if i == attempts - 1:
+                        raise
+                    else:
+                        time.sleep(1)
+                        continue
 
     def _clear_isolated_net_resources(self):
         client = self.routers_admin_client