Exposed $logroot_mode in init.pp

This commit now allows you to set the directory permissions on the $logroot
directory. It also resolves a catalog compilation issue when specifying the
apache class with default_vhost => false, and no other vhost resources.
@mhaskel this is true, but that resource also creates the default log directory (/var/log/httpd, or /var/log/apache). So when add `$ensure == 'present'` you're effectively making `default_vhost => false` useless, as Apache will fail to start if the log directory specified in httpd.conf (ErrorLog) doesn't exist. One way around this is to move the creation of the default log location to init.pp.