Optimized Driver SG logic could use some cleanup

[MattDietz]

It's a little hard to follow what's going on, and the rule count algorithm seems like it could improve pretty dramatically in efficiency

def _get_security_group(self, context, group_id):
    group = context.session.query(models.SecurityGroup).\
        filter(models.SecurityGroup.id == group_id).first()
    rulelist = {'ingress': [], 'egress': []}
    for rule in group.rules:
        rulelist[rule.direction].append(
            self._make_security_rule_dict(rule))
    return {'uuid': self._query_security_group(context, group_id).nvp_id,
            'logical_port_ingress_rules': rulelist['ingress'],
            'logical_port_egress_rules': rulelist['egress']}

def _check_rule_count_per_port(self, context, group_id):
    ports = context.session.query(models.SecurityGroup).filter(
        models.SecurityGroup.id == group_id).first().get('ports', [])
    groups = (set(group.id for group in port.get('security_groups', []))
              for port in ports)
    return max(self._check_rule_count_for_groups(
        context, (self._get_security_group(context, id) for id in g))
        for g in groups)