// Amazon's requirements (i.e. DNS naming conventions). It must be 3-63
// characters long, and it must be a sequence of one or more labels
// separated by periods. Each label can contain lowercase ascii
// letters, decimal digits and hyphens, but must not begin or end with
// a hyphen. See:
// http://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html
func IsValidBucketName(bucket string) bool {