Fix mount point for Watchtower

The auth file created by the registry login task doesn't need to be
stored in a non-default path.

roles/docker/tasks/services/docker_registry.yml

@@ -28,9 +28,8 @@
   args:
     creates: "{{ docker_registry.volume_folder }}/auth/htpasswd"
 
-- name: log in to local registry
+- name: log in to registry
   docker_login:
     registry: "{{ docker_registry.domain }}"
     username: "docker"
     password: "{{ docker_password }}"
-    config_path: "{{ docker_registry.volume_folder }}/auth/config.json"

roles/docker/tasks/services/watchtower.yml

@@ -9,5 +9,5 @@
     networks:
       - name: external_services
     volumes:
-      - /var/run/docker.sock:/var/run/docker.sock
-      - "{{ docker_registry.volume_folder }}/auth/config.json:/config.json"
+      - "/var/run/docker.sock:/var/run/docker.sock"
+      - "/root/.docker/config.json:/config.json:ro"