Fix docker group to append group rather than set it

tasks/docker-users.yml

@@ -3,4 +3,5 @@
   user:
     name: "{{ item }}"
     group: docker
+    append: yes
   with_items: "{{ docker_users }}"

tasks/main.yml

@@ -1,8 +1,8 @@
 ---
-- include: setup-RedHat.yml
+- include_tasks: setup-RedHat.yml
   when: ansible_os_family == 'RedHat'
 
-- include: setup-Debian.yml
+- include_tasks: setup-Debian.yml
   when: ansible_os_family == 'Debian'
 
 - name: Install Docker.
@@ -14,8 +14,8 @@
     state: started
     enabled: yes
 
-- include: docker-compose.yml
+- include_tasks: docker-compose.yml
   when: docker_install_compose
 
-- include: docker-users.yml
+- include_tasks: docker-users.yml
   when: docker_users