ftest: update generator to avoid go misinterpretation
ftest: update generator to avoid go misinterpretation

Go may warn (exit non-zero) in some cases because it interprets the
`^// +build` string fragment as a pragma. By moving this to the
beginning of the string, we can avoid the issue entirely.

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