💚 Fixed error 'ansible_user' is undefined.

ERROR:

```
The task includes an option with an undefined variable. The error was: 'ansible_user' is undefined
```

- ref. ansible/ansible#23530
- ref. geerlingguy/drupal-vm#1302

roles/docker/tasks/001_install-docker-ce.yml

@@ -26,7 +26,7 @@
   - name: Add user to docker group.
     user:
       #name: "{{ lookup('env', 'user') }}"
-      name: "{{ ansible_user }}"
+      name: "{{ ansible_env.SUDO_USER }}"
       groups: docker
       append: yes
 

roles/user/tasks/001_configure-sudo-for-working-users.yml

@@ -4,7 +4,7 @@
   template:
     src: sudoers.j2
     #dest: "/etc/sudoers.d/{{ lookup('env', 'USER') }}"
-    dest: "/etc/sudoers.d/{{ ansible_user }}"
+    dest: "/etc/sudoers.d/{{ ansible_env.SUDO_USER }}"
     owner: root
     group: root
     mode: 0440

roles/user/templates/sudoers.j2

@@ -1,3 +1,3 @@
-{{ ansible_user }} ALL=(ALL) NOPASSWD: ALL
-Defaults:%{{ ansible_user }} !requiretty
-Defaults:%{{ ansible_user }} env_keep += SSH_AUTH_SOCK
+{{ ansible_env.SUDO_USER }} ALL=(ALL) NOPASSWD: ALL
+Defaults:%{{ ansible_env.SUDO_USER }} !requiretty
+Defaults:%{{ ansible_env.SUDO_USER }} env_keep += SSH_AUTH_SOCK