net-mgmt/librenms: fix rc script restart race & log rotation

Please stop librenms service before updating. No harm will occur.
The value in the PID file changes from the service to the supervisor.

Behavior changes: "service librenms status" now reports the daemon(8)
supervisor PID instead of the python PID; log rotation now actually
re-opens the log file.

Upgrade note: an instance started with the previous rc script is
invisible to the new procname and still holds the pidfile lock. Stop
the service before upgrading, or SIGTERM the old supervisor (visible in
ps as "daemon: ..."), which cleanly terminates the child and removes
the pidfile.

PR: 298398