Fix drush_log usage in Provision/Config.php when using custom templates

When using a custom provision module to override tpl.php files (ex: for the vhost template), I ran into "could not convert object to string in database.inc".

Turns out it was a bad drush_log statement in Provision/Config.php. Perhaps a drush upgrade now triggers the error, before it didn't, because I've been using this custom provision module for at least a year, and never ran into this issue.

Patch incoming.