remote_daemon: Set shutdown callbacks only after init is done

remote_daemon: Set shutdown callbacks only after init is done

The initialization of drivers happens in a separate thread.
However, the main thread continues initialization and sets
shutdown callbacks (virStateShutdownPrepare() and
virStateShutdownWait()) even though the driver init thread is
still running. This is dangerous because if the daemon decides to
quit early (e.g. because SIGINT was delivered) the
shutdownPrepare and shutdownWait callback are called over
partially init drivers.

Set callbacks only after all drivers were initialized.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/218
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2027400

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>