Audit the error mapping

In CBSE-9857, it is noted that an LCB_ERR_SOCKET_CLOSED is coming through as a CouchbaseException, as we don't have a specific SocketClosedException. Ideally, we would look at the LCB error map, notice this is a network error, and throw a NetworkException here. This is a general problem, and ideally we can make a general solution that works like this, for errors that are not mapped to a specific exception.