Since the containers are no longer on the host list, they were not found
while provisioning, oops.
To fix, had to add to a host's info a map of the containers docked to it.
Unfortunately, that required Propellor.Types.Info be glommed into
Propellor.Types, since it needed to refer to Host.
The problem is it fell back to looking for an alias for the bad hostname,
but to get the aliases, it needs to know which hosts are docked where,
so looped.