Missing stemcell AMI image for AWS Asia Pacific (Seoul) region

[premist]

AWS launched Asia Pacific (Seoul) region this month. After modifying bosh-aws-cpi-release to have support for AWS Seoul region, I encountered another error related to stemcell.

Command 'deploy' failed:
  creating stemcell (bosh-aws-xen-hvm-ubuntu-trusty-go_agent 3012):
    CPI 'create_stemcell' method responded with error: CmdError{"type":"Bosh::Clouds::CloudError","message":"Stemcell does not contain an AMI for this region (ap-northeast-2)","ok_to_retry":false}

I created a PR(#1109) which adds ap-northeast-2 to the AWS region list, but I'm not sure which part I should look into in order to create a stemcell AMI image for the new region.

[dpb587-pivotal]

Light stemcells include AMIs for ap-northeast-2 as of 3189...

$ curl -s -L https://bosh.io/d/stemcells/bosh-aws-xen-hvm-ubuntu-trusty-go_agent?v=3189 | tar -xzOf- stemcell.MF | grep ap-northeast-2 | awk '{print $2}'
ami-37f63859

Related story: https://www.pivotaltracker.com/story/show/112368753