Change how BoltServerAddress equality works

[ali-ince]

BoltServerAddress was checking equality on Hostname, Resolved IP and Port triplet and DnsResolver was causing loss of original Hostname.

This commit removed public access to resolved IP Address component of BoltServerAddress and removes it from the equality check, thus resulting in same hostname:port pairs equal whatever IP address they are resolved to.

Also removed DnsResolver since it returns a set of addresses (which would not allow same hostname:port pairs resolved to different IP addresses) and offloaded the dns resolution to take place just after custom address resolution (default is identity resolver) happens.

[ali-ince]

For the record, we have discussed this PR with @zhenlineo and decided to merge it in.

The only behavioural change visible from outside will be that if the user provides a ServerAddressResolver implementation through configuration, the returned ServerAddresses will go through DNS resolution as well (and that resolution will resolve all IP addresses registered which will be tried in turn until successful). This only applies to initial routing table lookup and fallback to initial routing table when none of the known routers are accessible.