Add force-reload to upstart script

The LSB core spec specifies that all init scripts shall have a force-reload action that ensures that the configuration file is reloaded. This is often implemented by restarting the service. But as pm2 supports reloading configuration files without restarting, force-reload can just point to reload.
Merge pull request #538 from UnrealQuester/master

Add force-reload to upstart script