ServerName parsing from directory name should be more robust to errors from guava's HostAndPort

our internal Address facade over HostAndPort directly passes on any failures from the underlying Guava implementation. Right now when we parse a ServerName from a WAL directory we properly handle if guava gives us an IllegalArgumentException but we do not handle if it gives us a IllegalStateException. e.g. it uses the former for "I couldn't parse anything out of this string" and the latter for "I parsed a host name but didn't see a port".