Support authentication against Amazon ECR

[JeanRev]

Amazon EC2 registries (ECR) are using one-time-password issued through the AWS authentication service. They have a fixed lifespan of 12 hours, and must therefore be continuously refreshed.

Two options are considered:

1. Retrieving the username/password from the Docker credential store.
2. Querying AWS ourselves, using the ECR Java API (if the SDK is leightweight enough).

Depends on #7.

[syba4ever]

Hello, I discover this issue as I am currently looking for a way to pull agent image from AWS ECR. As a workaround, I was thinking of storing the AWS token in a param, refreshing it regulary via a build and then referencing the param in the docker password in the cloud profile configuration. Unfortunately, the docker user and password do not support referencing params.
Is there any way to dowload agent image from AWS ECR, please?