ATS' tracking of host failures is broken for entries acquired through the hosts file

The current implementation of the hosts file maintains a map of name to hostdbinfo, which means that any lookups that come into the probe method return the same hostdbinfo struct. This means that any requests to a given address (regardless of port) recieve the same HostDBInfo struct-- which in turn means that the up/down status is global to the IP instead of per ip/port pair.