Make sure to remove 'install' directory if wallabag is already installed

Subsequent runs of wallabag's playbook result in the 'install' directory being
recreated, (after the "Clone wallabag" step) kicking wallabag's first time
setup procedure.

With this patch we automatically remove the 'install' directory if wallabag's
configuration file appears to be in place before cloning the repository.

roles/readlater/tasks/wallabag.yml

@@ -1,8 +1,16 @@
+- name: Determine whether wallabag is configured
+  stat: path=/var/www/wallabag/inc/poche/config.inc.php
+  register: wallabag_config
+
 - name: Clone wallabag
   git: repo=https://github.com/wallabag/wallabag.git
        dest=/var/www/wallabag
        version={{ wallabag_version }}
 
+- name: Remove wallabag 'install' directory if its configuration file is there
+  file: name=/var/www/wallabag/install state=absent
+  when: wallabag_config.stat.exists == True
+
 - name: Install wallabag dependencies
   apt: pkg={{ item }} state=present
   with_items: