ONOS "service" configuration files

In order to run ONOS as a "service," whose execution is managed
by the OS, you can install an appropriate configuration/startup file.

onos.initd:     startup file for SysV/init.d-based systems
                usually installed as /etc/init.d/onos

onos.conf:      configuration for upstart-based systems
                usually installed as /etc/init/onos.conf

onos.service:   configuration for systemd-based systems
                currently calls /etc/init.d/onos start
                usually installed as /etc/systemd/system/onos.service

The reason why onos.service currently calls /etc/init.d/onos
is because the init.d script fixes permissions that are required
by onos-service (such as /opt/onos/apps.)
