Handle host discovery in clusters with IPv6 addresses

Cassandra doesn't wrap IPv6 addresses in brackets when querying system.peers, and the old method of checking for a port appended to the address didn't account for the extra colons in IPv6 addresses.
Cleaner address/port parsing
Don't change file permissions
Merge pull request #285 from SilentCircle/ipv6_discovery

Handle host discovery in clusters with IPv6 addresses