Change log level to info rather than warn

[geoffharcourt]

Attempting to create a job that isn't unique shouldn't be such an important event that it shows up as a warning in the logs. I think the ability to log the attempts is great, but I think the value isn't there unless you're engaged in a level of diagnosis in which you're checking logs at the info or debug levels. Could we switch the logging level to be info?

Happy to do the PR to make the change if there's agreement.

[mhenrixon]

Closed by #81