Use Munin plugins configuration to setup a few basic stuff

[ywarnier]

Check https://github.com/munin-monitoring/contrib/blob/master/plugins/drupal/drupal_files_total.php for an example on how to get those settings.

[ywarnier]

For example, one required setting is the $sub variable in the plugins, which is set by default to '/www', while sometimes it should just be ''.
Also, the root dir needs to be configurable in case it is not /var/www

[ywarnier]

There is an additional problem with the paths defined in the _proxy.php scripts, whereas we define /root/php/ as a hardcoded path to find the scripts. Should be replaced by DIR or something like that (not necessary to use munin config for that)