Added Systemd support fix #619
Fix some typo in archipel.conf
Improve the init script

Look for systemd, fallback on init.d, error message is no match found
Fix a path issue and rename service to archipel-agent
Merge branch 'agent-compatibility-improvements' of https://github.com/CyrilPeponnet/Archipel into pr-668
Update the typo HOSTAME where is used