Add --reload command-line parameter.

Refs #5788
Fork new process from previous daemon on reload.

The previously planned logic of forking a new daemon from the reload-process didn't work with
systemd: systemd does not allow long-running processes started from within the reload command.

Replaces parameter --reload with --reload-internal which is used when starting the new daemon.

Refs #5788
Fix logging during shutdown procedure.

Refs #5788