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.
@igalic do you see this change causing any issues?  I'm not sure I like this as it will create the logroot directory even if you're deleting the vhost.