chore(contrib/*): update to CoreOS 324.2.0

One minor fix to CoreOS here: http://coreos.com/releases/#324.2.0

Double-check the IDs:
EC2: https://coreos.com/docs/running-coreos/cloud-providers/ec2/
Rackspace: https://coreos.com/docs/running-coreos/cloud-providers/rackspace/ (N/A)