func (c *ec2MetadataClientImpl) SubnetID(mac string) (string, error) {
	return c.client.GetMetadata(fmt.Sprintf(SubnetIDResourceFormat, mac))
}
func (c *ec2MetadataClientImpl) SubnetID(mac string) (string, error) {
	return c.client.GetMetadata(fmt.Sprintf(SubnetIDResourceFormat, mac))
}
// SubnetID returns the subnet id for the network interface,
// given its mac address