Change JobWithTimeout to contain instance of job

[jhidding]

This change would better fit the underlying OOP design.

[sverhoeven]

scheduler.wait_until_done(job=job, timeout=1000)

of OOP

job = scheduler.submit_batch_job(...)
job.wait_until_done(42)

[jspaaks]

At some point I had a discussion with Jason / @jmaassen about the OOP'ness (of Java Xenon) where this point came up. Our conclusion back then was that it makes more sense to limit OOPness to some toplevel objects.

In other words

• scheduler.waituntildone yes
• job.waituntildone no

[jhidding]

Ok, we'll keep it like it is.