chore(*): update base CoreOS to 494.5.0

Includes Docker 1.3.3 with several security fixes.
See https://coreos.com/releases/#494.5.0 and #2729.

Double-check IDs at https://coreos.com/docs/running-coreos/cloud-providers/ec2/ and https://coreos.com/docs/running-coreos/cloud-providers/google-compute-engine/.