Add Ansible role to fix Drupal file permissions

Add a new `drupal-permissions` Ansible role that resets the file and
directory permissions to match the ones described in
https://www.drupal.org/node/244924.

This will later be released to Ansible Galaxy, but for now it will
remain in this repository until the required changes are made and the
appropriate documentation is added.

Fixes #191

tools/ansible/roles/drupal-permissions/tasks/main.yml

@@ -0,0 +1,29 @@
+---
+- name: Set the permissions for each Drupal root directory.
+  file:
+    group: www-data
+    mode: ug=rX,o=
+    owner: "{{ drupal_permissions.user }}"
+    path: "{{ item.root }}"
+    recurse: true
+    state: directory
+  with_items: "{{ drupal_permissions.sites }}"
+
+- name: Set permissions for the defined settings files.
+  file:
+    mode: a-X
+    path: "{{ item.0.root }}/{{ item.1 }}"
+    state: file
+  with_subelements:
+    - "{{ drupal_permissions.sites }}"
+    - settings_files
+
+- name: Set permissions for the defined files directories.
+  file:
+    mode: ug=rwX,o=
+    path: "{{ item.0.root }}/{{ item.1 }}"
+    recurse: true
+    state: directory
+  with_subelements:
+    - "{{ drupal_permissions.sites }}"
+    - files_directories