ansible/docuum: fix docker_max_image_space replace

When changing the value, replace the previous line instead of adding a
new line at the bottom.

Related: OS#5099
Change-Id: I35a3671a026cc72cf1488c8668e8a0e675de2530

ansible/roles/docker/tasks/docuum.yml

@@ -5,6 +5,7 @@
     state: present
     create: yes
     line: "{{ docker_max_image_space }}"
+    regexp: ".*"  # replace previous content if changed
 
 - name: "docuum : copy Dockerfile"
   copy: