Private docker images

Launch Template :
```
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="==MYBOUNDARY=="

--==MYBOUNDARY==

Content-Type: text/x-shellscript; charset="us-ascii"

#!/bin/bash
echo ECS_IMAGE_CLEANUP_INTERVAL=60m >> /etc/ecs/ecs.config
echo ECS_IMAGE_MINIMUM_CLEANUP_AGE=60m >> /etc/ecs/ecs.config
export DOCKER_USERNAME=boomtable
export DOCKER_PASSWORD=xyz
docker login --username $DOCKER_USERNAME --password=$DOCKER_PASSWORD
--==MYBOUNDARY==--

```

Error while triggering the batch job !

```
Status reason

Task failed to start

Container message

CannotPullContainerError: Error response from daemon: pull access denied for myprivate/testbatch, repository does not exist or may require 'docker login'
```

Am i doing anything stupid !? is this a right way to do it ?

Begin with the Launch Template user-data, the ECS config entries, the docker login command, and the AWS Batch job startup error. Compare the image-pull authentication setup with the reported CannotPullContainerError and determine the documented configuration path; done means the batch job can start its private image without that error.

Written by the indexing model from the issue text.