wait is used for two purposes:
- check that the instances have effectively started
- get the data (public ip, etc) from the instance once it has started - which we don't have immediately.

The behavior of amazon's ruby API is to redo an API each time we look for the object's members.
So basically, if we do a print_run_info without waiting, we will
- do an extra 2 x number of instances API requests to Amazon that are useless, and add latency,
- not get any data anyway, it's too early