Changes to Retrieve status of a create certificates task.

api operation id getBulkCertificatesTaskStauts removed and replaced with getCertificatesTask

added the media type application/vnd.aws-cdf-v1.0+json for the response with the status 200

added the media type application/vnd.aws-cdf-v1.0+json for the response with the status 404

removed the non-success response with the status 400