Split out hosts config deployment

This patch moves the hosts configuration into its own deployment.
It will continue to use os-apply-config as something that is
required early on in the bootstrapping (it needs to be
configured before puppet runs for example).

The motivation here is so we can refactor all-nodes-config.yaml to use a
new hiera hook that that avoids os-apply-config entirely.

Change-Id: Ib3e4380f205358b27d22a1102b663cf300b1ed86
Partial-bug: #1596373

hosts-config.yaml

@@ -0,0 +1,30 @@
+heat_template_version: 2016-10-14
+description: 'All Hosts Config'
+
+parameters:
+  hosts:
+    type: comma_delimited_list
+
+resources:
+
+  hostsConfigImpl:
+    type: OS::Heat::StructuredConfig
+    properties:
+      group: os-apply-config
+      config:
+        hosts:
+          list_join:
+          - "\n"
+          - {get_param: hosts}
+
+outputs:
+  config_id:
+    description: The ID of the hostsConfigImpl resource.
+    value:
+      {get_resource: hostsConfigImpl}
+  hosts_entries:
+    description: |
+      The content that should be appended to your /etc/hosts if you want to get
+      hostname-based access to the deployed nodes (useful for testing without
+      setting up a DNS).
+    value: {get_attr: [hostsConfigImpl, config, hosts]}