container: reset variables in role init, define more defaults outside tasks

roles/container/tasks/init.yml

@@ -1,12 +1,18 @@
 ---
 
+- name: Reset variables
+  set_fact:
+    docker_volume_definition: []
+    container_published_ports: []
+    final_docker_volumes: "{{ docker_volumes }}"
+
 - name: Set docker service full name
   set_fact:
     docker_service_name: "{{ docker_service }}_{{ docker_service_suffix }}"
   when: docker_service_suffix is defined
 
 - name: Convert docker_volumes from legacy format
-  when: docker_volumes is defined and docker_volumes[0] is not mapping
+  when: docker_volumes | length > 0 and docker_volumes[0] is not mapping
   block:
     - name: Warn about docker_volumes legacy format
       debug: