cico: use duffy for system reservation and returning

We directly reserve a session and the number of machines we want. This should avoid starving when one machine out of two is reserved and we are waiting for the second blocking the first one.

Build now doesn't use another machine (as the machine number limit is 10). but is performed on the machine[0].

Returning machine is left to groovy script and returns the whole session with all machines at once.

Yes, we have a public hostname again.