Resolve names to all dns records (multiple dns A records)

This applies to all drivers, not just the Java one.

At present, to connect, a client must provide a driver with a connection string that specifies one or more members of a replica set. This is fragile, because if the string only specifies one host, and that host is down, then the client can't connect. At the other extreme, if the members of the replica set are in flux, or change, then the client must constantly have to use different connection strings.

Instead, it is suggested that we have the means to use a DNS lookup to find the members of a replica set. Instead of providing a list of hosts to the driver, provide a DNS name, for all of them. The driver does a DNS lookup, obtaining a set of A records, and starts trying those for the primary connection. This means that adding, moving, or removoing servers can still work if the number and absolute IP addresses change. The administrator need only adjust the DNS entries.