Comment 1 for bug 1842460

The create cell task doesn't fail on multiple invocations, because the `Create base cell for legacy instances` task has ` '"already exists" not in nova_cell.stdout'` in the failed_when conditions. The output when re-registering the base cell is for example:
 `The specified transport_url and/or database_connection combination already exists for another cell with uuid f6725b18-841d-40a1-b91d-7568d7440516.`