ecs + custom stack name

[kc-dot-io]

overview

when using a custom stack name, the docker ecs image does not properly report back to the correct ci instance on github because it was hard coded to the default value

tasks

• infer the ci instance from stack name
• build and push new docker image to slajax/lambci
• build and test with slajax/lambci and ecs + custom stack name lambci#91
• build and push new docker image to lambci/ecs

closes #17

[riderx]

need this one !