Deploy Stemcell builder pipeline to e/w

[dlapiduz]

In order to have parity between the environments and pipelines we need to deploy the stemcell builder job (https://github.com/18F/cg-aws-light-stemcell-builder) to e/w.

Acceptance Criteria

• [x] Pipeline is created in ci.cloud.gov
• [x] At least one stemcell is uploaded to an S3 bucket in us-east

[jmcarp]

Pipeline is running at https://ci.cloud.gov/pipelines/aws-light-stemcell-builder, and stemcells are getting published to the cg-ew-stemcell-builder bucket.

[mogul]

Confirmed in use.