Previously when a domain would get stuck in a domain job due to a
programming mistake we'd report the following control state:
$ virsh domcontrol domain
occupied (1424343406.150s)
The timestamp is invalid as the monitor was not entered for that domain.
We can use that to detect that the domain has an active job and report a
better error instead:
$ virsh domcontrol domain
error: internal (locking) error
31a55c7cb4