manage not found domain in EventManager

The EventManager is notified for all events from all domains managed by Libvirt
even if they are not members of the testbed managed by the instance Cloubed.
In this case, simply ignore the event.
move http server start from boot_vm to wait_event

HTTPServer is actually used while Cloubed waits for event. It is therefore way
better to start the server before waiting for event instead of just after
booting a domain.
make wait action work in cli + remove --wait-event

Make wait action work in Cloubed CLI script. Remove now useless argument
--wait-event for boot action.
adapt debian example shell script for wait event

The shell script that gives an example of cloubed CLI script usage for
installing a minimal Debian VM has been adapted for using new working wait
action. Also avoid using removed argument --wait-event with boot action.