This is the first step to implement CI for websites.

It introduce a new script tools/build_all.sh which build all active websites in one place (inside the out directory), and can then be served by httpd.
In case one of the site is failing to build, you'll find the build log (build.log) in its own directory, and accessible through the web server.
Additionally, to be able to host each site in a subdirectory, I added the basepath override (variable ${path}) where it was missing.

Thanks to this script, CI can be automatically triggered to give contributors a preview of their changes for each PR.
Preview like this one : https://pr1112-fedora-web-ci.apps.ocp.ci.centos.org/
Build log is available for each site, whatever the build is a success or not. Example for spins : https://pr1112-fedora-web-ci.apps.ocp.ci.centos.org/spins.fedoraproject.org/build.log

Preview is updated every time the corresponding PR is updated or rebased.
Once the PR is merged or closed, the preview site is removed.
At this time, there is also a time limit of 2 weeks, after which it is also deleted.

This PR has already been merged on staging, to make sure nothing break when not using the basepath override.