Dockerized ecs-deploy application

This provides a CI friendly Docker wrapper for silinternational/ecs-deploy.

To use, replace ecs-deploy in the README examples as follows:

ecs-deploy -c production1 -n doorman-service -i docker.repo.com/doorman:latest

... becomes:

docker -v ~/.aws:/root/.aws run swissarmyronin/ecs-deploy \
    -c production1 -n doorman-service -i docker.repo.com/doorman:latest

... or:

docker -e AWS_ACCESS_KEY_ID=<<access_key_id>> \
    -e AWS_SECRET_ACCESS_KEY=<<secret_access_key>> \
    -e AWS_DEFAULT_REGION=eu-west-1 \
    run swissarmyronin/ecs-deploy \
        -c production1 -n doorman-service -i docker.repo.com/doorman:latest

Providing the key and secret as parameters for ecs-deploy with -k and -s doesn't work as of version 3.6.0 of ecs-deploy.