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.
Seems like there's a link missing ..