hostname: Also write /etc/hosts

This commit introduces a new role, *hostname*, that is used by the
`hostname.yml` playbook to set the hostname. It also writes
`/etc/hosts` using a template.

hostname.yml

@@ -1,5 +1,3 @@
 - hosts: all
-  tasks:
-  - name: ensure hostname is set
-    hostname:
-      name={{ preferred_hostname|d(inventory_hostname) }}
+  roles:
+  - hostname

roles/hostname/defaults/main.yml

@@ -0,0 +1 @@
+preferred_hostname: '{{ inventory_hostname }}'

roles/hostname/tasks/main.yml

@@ -0,0 +1,8 @@
+- name: ensure hostname is set
+  hostname:
+    name={{ preferred_hostname }}
+- name: ensure hosts file is populated
+  template:
+    src=hosts.j2
+    dest=/etc/hosts
+    mode=0644

roles/hostname/templates/hosts.j2

@@ -0,0 +1,2 @@
+127.0.0.1   {{ preferred_hostname }} {{ preferred_hostname.split('.')[0] }} localhost localhost.localdomain localhost4 localhost4.localdomain4
+::1         {{ preferred_hostname }} {{ preferred_hostname.split('.')[0] }} localhost localhost.localdomain localhost6 localhost6.localdomain6