core/manager: Make sure jobs statistics are not double after daemon-reload

core/manager: Make sure jobs statistics are not double after daemon-reload

We add n_installed_jobs and n_failed_jobs to our inner state after
deserialization. This is fine during daemon-reexec when we start with clear
Manager (and some jobs possibly queued before deserialization), however,
daemon-reload works with the same manager and adding the values would
effectively double the counters. Reset the counters before we deserialize and
add their values again.