START_TIMEOUT ignored when run from systemd

NMS-12769 introduced an option to the service script, -s, which when utilized plays better with systemd, but it also ends execution of the script with an exit 0 prior to the handling of the START_TIMEOUT option. This doesn't seem necessary especially given the continued existence of the -Q option to override the value present in $ONMS_HOME/etc/opennms.conf, as IMO there are valid reasons to want to let the service start up completely before returning.