<httpd carts> bug 1060068: ensure extra httpd conf dirs exist

https://bugzilla.redhat.com/show_bug.cgi?id=1060068
httpd cartridges won't see new /etc/openshift/cart.conf.d dirs when restarted
Merge pull request #4632 from sosiouxme/custom-httpd-confs

Merged by openshift-bot