feat(pipelines): install Docker in test_commands CodeBuild project

[huanjani]

If users have their tests configured in containers, they can now use docker build commands in the test_commands field of the pipeline manifest.

Addresses #1280.

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[bvtujo]

Looks great! Do we need to update any integration tests for this?

[huanjani]

Looks great! Do we need to update any integration tests for this?

They're passing locally. I updated the stack/pipeline ones. It'd be nice to eventually test containerized tests where we test test_commands.

[ceagan]

Suggestion: the environment variable for the AWS_ACCOUNT_ID can also be exposed here like it is for the main build. It could be helpful when pulling images from an ECR private repository, which in turn is helpful to avoid Docker Hub pull limits.

        EnvironmentVariables:
          - Name: AWS_ACCOUNT_ID
            Value: !Sub '${AWS::AccountId}'

[ceagan]

I was able to pull these changes and test with a sandbox build I've been working on and it works perfectly! Thanks!

[huanjani]

Suggestion: the environment variable for the AWS_ACCOUNT_ID can also be exposed here like it is for the main build. It could be helpful when pulling images from an ECR private repository, which in turn is helpful to avoid Docker Hub pull limits.

        EnvironmentVariables:
          - Name: AWS_ACCOUNT_ID
            Value: !Sub '${AWS::AccountId}'

Thanks for this suggestion (and for your Gitter post that got this ball rolling)!