manager: split out send_ready and basic.target checking into functions of their own

manager: split out send_ready and basic.target checking into functions of their own

Let's shorten manager_check_finished() a bit by splitting out checking
of basic.target and the two things we do when we reach it.

This should not change behaviour, except for one thing: we now check
basic.target's actual state for figuring out whether it is up, instead
of generically checking whether it has any job queued. This is arguably
more correct, and is what other code does too for similar purposes, for
example manager_state()