Writes a foreman rule to the database.

def WriteForemanRule(self, rule, cursor=None):
    """Writes a foreman rule to the database."""
    query = ("INSERT INTO foreman_rules "
             "  (hunt_id, expiration_time, rule) "
             "VALUES (%s, FROM_UNIXTIME(%s), %s) "
             "ON DUPLICATE KEY UPDATE "
             "  expiration_time=FROM_UNIXTIME(%s), rule=%s")

    exp_str = mysql_utils.RDFDatetimeToTimestamp(rule.expiration_time),
    rule_str = rule.SerializeToString()
    cursor.execute(query, [rule.hunt_id, exp_str, rule_str, exp_str, rule_str])