etc-git: add a task to commit

It can be invoked in pre/post tasks or anywhere in anther role.

etc-git/README.md

@@ -4,4 +4,28 @@ Put /etc under Git version control.
 
 ## Tasks
 
-Everything is in the `tasks/main.yml` file.
+The main part (installation and configuration) is in the `tasks/main.yml` file.
+
+There is also an independant task that can be executed to commit changes made in `/etc/.git`, for example when a playbook is run :
+
+```
+- name: My Splendid Playbook
+  […]
+
+  pre_tasks:
+  - include_role:
+      name: etc-git
+      task_from: commit.yml
+    vars:
+      commit_message: "Ansible pre-run my splendid playbook"
+
+  roles :
+  […]
+
+  post_tasks:
+  - include_role:
+      name: etc-git
+      task_from: commit.yml
+    vars:
+      commit_message: "Ansible pre-run my splendid playbook"
+```

etc-git/defaults/main.yml

@@ -0,0 +1,2 @@
+---
+commit_message: Ansible run

etc-git/tasks/commit.yml

@@ -0,0 +1,33 @@
+---
+- name: is /etc clean?
+  command: git status --porcelain
+  args:
+    chdir: /etc
+  changed_when: False
+  register: git_status
+  when: not ansible_check_mode
+  ignore_errors: yes
+  tags:
+  - commit-etc
+
+- debug:
+    var: git_status
+    verbosity: 3
+  tags:
+  - commit-etc
+
+- name: /etc modifications are committed
+  shell: "git add -A . && git commit -m \"{{ commit_message | mandatory }}\""
+  args:
+    chdir: /etc
+  register: etc_commit_end_run
+  when: not ansible_check_mode and git_status.stdout != ""
+  ignore_errors: yes
+  tags:
+  - commit-etc
+
+- debug:
+    var: etc_commit_end_run
+    verbosity: 4
+  tags:
+  - commit-etc