tasks: horizon_post_install: Add 'force' parameter when creating symlink

A local_settings.py may already exist as a regular file so in that case
we need to use the 'force' parameter to force the symlink creation.

Change-Id: I05eb9026707639aa12ea1c3ae93b872191528069

tasks/horizon_post_install.yml

@@ -56,6 +56,7 @@
     owner: "{{ horizon_system_user_name }}"
     group: "{{ horizon_system_group_name }}"
     state: "link"
+    force: yes
   with_items:
     - { src: "/etc/horizon/local_settings.py", dest: "{{ horizon_lib_dir }}/openstack_dashboard/local/local_settings.py" }