Support for CoreOS Container Linux instead of Taupage AMI

[hjacobs]

We are running the etcd appliance for our Kubernetes setup and would like to switch to CoreOS Container Linux as it would remove one dependency for us (Kubernetes nodes already run Container Linux).

It should be relatively simple to provide another Cloud Formation / Senza file with CoreOS Container Linux instead of Taupage (in the end we are just running a Docker container).

[szuecs]

We switched to Ubuntu, so this can be closed