Tests for:
* ecs_cluster
* ecs_service
* ecs_service_facts
* ecs_taskdefinition
* ecs_taskdefinition_facts
* Add idempotency testing
Test ecs_cluster, ecs_service and ecs_taskdefinition for trivial
idempotency. Add FIXMEs to the tests because the latter two fail.
Remove unused dependencies
