chore(coreos): upgrade to 379.3.0

This also bumps Docker to 1.1.1.

Note that this also changes the AMI block devices, as CoreOS changed
this recently: https://github.com/coreos/scripts/commit/4cd9ed45ff274536bff68feda1979b32e497ddb2#diff-25d2735cfb71ea69567722f7ded269b1R187