Fetches the security group.

        :returns: SecurityGroup object corresponding to sg_id

def get(self, sg_id):
        """Fetches the security group.

        :returns: SecurityGroup object corresponding to sg_id
        """
        secgroup = self.client.show_security_group(sg_id).get('security_group')
        sg_dict = self._sg_name_dict(sg_id, secgroup['security_group_rules'])
        return SecurityGroup(secgroup, sg_dict)