Automatic merge from submit-queue

AWS: Add support for ap-northeast-2 region (Seoul)

This PR does:
- Support AWS Seoul region: ap-northeast-2. 
Currently, I can not setup Kubernetes on AWS Seoul.  
Error Messages: 

> 
> ip-10-0-0-50 core # docker logs 0697db
> I0419 07:57:44.569174       1 aws.go:466] Zone not specified in configuration file; querying AWS metadata service
> F0419 07:57:44.570380       1 controllermanager.go:279] Cloud provider could not be initialized: could not init cloud provider "aws": not a valid AWS zone (unknown region): ap-northeast-2a