Set the CIVICRM_SETTINGS vhost env variable

[mlutfy]

The civimail open/click-through scripts cannot find the civicrm.settings.php file. The simplest workaround I could find is to set the CIVICRM_SETTINGS env variable in the vhost.

Ex:

SetEnv CIVICRM_SETTINGS /srv/aegir/platforms/wordpress-4.4/sites/example.org/wp-content/plugins/civicrm/civicrm.settings.php

This should be added systematically.