ECS configuration should set ECS_AVAILABLE_LOGGING_DRIVERS with awslogs

[joeshaw]

From http://docs.aws.amazon.com/AmazonECS/latest/developerguide/using_awslogs.html:

If you are not using the Amazon ECS-optimized AMI (with at least version 1.9.0-1 of the ecs-init package) for your container instances, you also need to specify that the awslogs logging driver is available on the container instance when you start the agent by using the following environment variable in your docker run statement or environment variable file. For more information, see Installing the Amazon ECS Container Agent.

ECS_AVAILABLE_LOGGING_DRIVERS=["json-file","awslogs"]

It would be nice if this worked out of the box on OpsWorks instances by setting it in https://github.com/aws/opsworks-cookbooks/blob/release-chef-11.10/opsworks_ecs/templates/default/ecs.config.erb