Install owncloud with owncloud-files package

The `owncloud` metapackage also installs dependencies such as Apache.
To avoid version problems, just install ownCloud.

roles/owncloud/tasks/owncloud.yml

     - dependencies
 
 - name: Install ownCloud
-  apt: pkg=owncloud update_cache=yes
+  apt: pkg=owncloud-files update_cache=yes
   tags:
     - dependencies