celery_backend: more robust queue length management
- Ignore the absence of the rabbitmq management interface
- Handle inexistent queues as if they were empty
Depends on !21 (closed)
Test Plan
tox
Migrated from D849 (view on Phabricator)
Staging instance, all changes can be removed at any time
Depends on !21 (closed)
tox
Migrated from D849 (view on Phabricator)