Change default RedHat confdir

RedHat sticks all mods/confs/vhosts in `$confdir/conf.d` but Debian sticks them in separate directories. Previosly the Apache module simulated Debian style conf dirs on RedHat, but this leads to confusing purging and updating with respect to configs that are added to `conf.d` by packages.

Changing the default to `conf.d` means that configs placed by packages are updated rather than ignored or purged. Also if purging is turned off this will not cause undesired config declarations.