nova: use any_errors_fatal for once-per-cell tasks

We run some nova tasks once per cell, using a condition to match a
single host in the cell. In other similar tasks, we use run_once, which
will fail all hosts if the task fails. Typically these tasks are
critical, and that is desirable. However, with the approach used in
nova-cell to support multiple cells, if a once-per-cell task fails, then
other hosts will continue to execute, which could lead to unexpected
results.

This change adds any_errors_fatal to the plays or blocks that run these
tasks.

Closes-Bug: #1948694

Change-Id: I2a5871ccd4e8198171ef3239ce95f475f3e4b051

ansible/nova.yml

@@ -71,6 +71,8 @@
     - nova-cell
     - nova-cell-bootstrap
   serial: '{{ kolla_serial|default("0") }}'
+  # Fail all hosts if any of these once-per-cell tasks fails.
+  any_errors_fatal: true
   tasks:
     # * Create nova cell DBs & users
     # * Create RabbitMQ vhost & user
@@ -259,6 +261,8 @@
     - nova-online-data-migrations
     - nova-cell-online-data-migrations
   serial: '{{ kolla_serial|default("0") }}'
+  # Fail all hosts if any of these once-per-cell tasks fails.
+  any_errors_fatal: true
   tasks:
     - import_role:
         name: nova-cell

ansible/roles/nova-cell/tasks/discover_computes.yml

@@ -19,3 +19,5 @@
 
   # Delegate to a cell conductor.
   delegate_to: "{{ groups[nova_cell_conductor_group][0] }}"
+  # Fail all hosts if any of these once-per-cell tasks fail.
+  any_errors_fatal: true