When adding a subscription in SubscribeUserJob, if an error caused by the feed server is raised (404 response, timeout, unable to resolve FQDN...) do not mark the job as failed.

Instead rescue the error, log it and mark the job as finished.

We are not interested in having resque jobs marked as failed because of external servers not being available. This is not an error condition but rather an expected and recoverable condition that will be managed.