Add CoreOS task to Razor

Allowing for full clusters of CoreOS to be deployed, automatically configuring the setup with heavy use of Razor's node-metadata function to enable features like etcd configuration, fleet metadata, formatting of drives and automatic addition of SSH keys. Since the node-metadata is applied on all nodes by the policy, their values can easily be updated with different settings on a per-node basis if wanted.

Uses two boot tasks, boot_install and boot_again:
boot_install will format a drive for persistent storage and mark the node as installed, then reboot
boot_again will be used during all boots after the node has been marked as installed

Documentation of the task added in the directory as well per discussions earlier on IRC.