Validate an account_id

def validate(self, meta, val):
        """Validate an account_id"""
        val = string_or_int_as_string_spec().normalise(meta, val)
        if not regexes['amazon_account_id'].match(val):
            raise BadOption("Account id must match a particular regex", got=val, should_match=regexes['amazon_account_id'].pattern)
        return val