Make containers stopped after the linked containers stopped

[snowhork]

Summary

This PR is for #474
Make containers stopped after the linked containers stopped.

Implementation details

When a container is stopped, check if other containers linking to the container have already stopped.

Volume dependency is not required to be checked because even if the volume container is stopped, other container can use the volume.

Testing

• Builds on Linux (make release)
• Builds on Windows (go build -out amazon-ecs-agent.exe ./agent)
• Unit tests on Linux (make test) pass
• Unit tests on Windows (go test -timeout=30s ./agent/...) pass
• Integration tests on Linux (make run-integ-tests) pass
• Integration tests on Windows (.\scripts\run-integ-tests.ps1) pass
• Functional tests on Linux (make run-functional-tests) pass
• Functional tests on Windows (.\scripts\run-functional-tests.ps1) pass

New tests cover the changes: yes

Description for the changelog

Make containers stopped after the linked containers stopped

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[snowhork]

This PR is for #474, but recently, ECS-team seems to address this problem (aws/containers-roadmap#123), so I wonder if this PR is acceptable.
If so, I will complete all testing and request review as soon as possible.

[sharanyad]

@snowhork thank you for your efforts on this PR. As you mentioned, we are currently working on code changes that include more than just the termination order but also the start order of containers based on dependencies in an ECS task. We are sorry that we could not accept this PR at this moment. Please watch out this branch https://github.com/aws/amazon-ecs-agent/tree/container-ordering-feature for updates on this feature.