Old node images are not being cleaned up when new ones are created #98
Description
When a new node image (AMI) was created with sudo /usr/local/bin/run-packer, the old node image is left behind, even though it's not used anymore (at least in AWS it is).
When building a new node image was successful, the previous node image should be deleted (deregistered in AWS terms).
I guess this is related to #95 (perhaps even a duplicate? not sure...)