gogenerate/awssdk: add an import step
gogenerate/awssdk: add an import step

Invoke 'goimports' while generating sdk artifacts. Generated targets
were missing some imports and this fixes that issue.

Also, refactored the code a bit to reduce duplication.

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