Update S3Gateway and S3Repository to add ap-northeast

It seems that S3Gateway and S3 Repository do not support ap-northeast-1.

FYI: And also document should be updated here http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-discovery-ec2.html

> The cloud.aws.region can be set to a region and will automatically use the relevant settings for both ec2 and s3. The available values are: us-east-1, us-west-1, ap-southeast-1, eu-west-1.