httpd cartridges: OVERRIDE with custom httpd conf

bug 1065533
https://bugzilla.redhat.com/show_bug.cgi?id=1065533
Implementation of bz 1054918 was intended to allow sysadmins to
override cartridges confs if needed. It didn't. This does.
Merge pull request #4771 from sosiouxme/custom-httpd-confs

Merged by openshift-bot