Monitor number of stale services

[jplitza (Jan-Philipp Litza)]

@andreas-doehler

Inside RAW edition setups it is very common that after a core restart you have to wait for 4 or 5 check cycles until all services are checked a first time.

This is mostly caused by the default setting max_service_check_spread=5 in ~/etc/nagios/nagios.d/tuning.cfg. Setting it to 1 greatly reduces this staleness period.