Arvados

1. access the container log endpoint while waiting for the container to finish, to make sure it returns a valid response (due to races, it's not necessarily an error if it can't get any actual log data before the container finishes, but it's an error if it receives a 502 error at any point during the container lifecycle, for example).
2. access the container log endpoint after the container has finished, to make sure the controller→webdav communication works correctly.

It is possible for a cluster to be misconfigured such that logs work only for unfinished containers, or only for finished containers, so diagnostics should do its best to check for both problems.