Adding appropriate failure message if image pulling fails
Adding appropriate failure message if image pulling fails

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