CHANGED set CONTAINER/PORT/URL before post-deploy

Once we completed check-deploy, we agree the new container is good to
go. And once we started running post-deploy hooks, there’s no automatic
recovery. So:

1. Commit to post-deploy completion by disabling kill_new trap after
check-deploy
2. Set CONTAINER/PORT/URL so post-deploy scripts can use them
3. Nginx post-deploy hooks gets the final say on the value of URL