add a note to add awsvpc mode tests to existing functional tests
add a note to add awsvpc mode tests to existing functional tests

aws/amazon-ecs-agent,aws/amazon-ecs-agent,aws/amazon-ecs-agent,swipely/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,swipely/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,aws/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent