unpack_dvd does not (re-)create modular repos/streams for EL8 dnf repos

We don't yet know how to create dnf module mirrors, particularly mirroring only some packages from a larger module/stream or automatically creating local module repositories from the contents of OS ISOs, like unpack_dvd does for traditional yum repositories.

Relevant links:

• https://bugzilla.redhat.com/show_bug.cgi?id=1801747

• https://github.com/rpm-software-management/modulemd-tools/

I replaced the unpack_dvd-created AppStream/repomd directory with the CentOS 8 ISO's AppStream/Packages/repomd directory on (instead of whacking it with unpack_dvd's createrepo .}}—but it results in the same errors when installing {{httpd.

Using the createrepo_c/modifyrepo_c commands to manage these modular repos (https://docs.fedoraproject.org/en-US/modularity/hosting-modules/), I got the module data working by doing the following:

After this point, an EL8 agent that had been failing to install httpd succeeded.

UPDATE: However, re-kicking the EL8 agent's box over PXE now fails; investigating...

On EL7, the createrepo_c and createrepo_c-libs packages are needed to run the commands above. These packages come from the CentOS Extras repo, and are not yet included with the SIMP 6.5 ISO.

On EL6, the createrepo_c and createrepo_c-libs packages are needed to run the commands above. These packages come from the EPEL6 repo, and are not yet included with the SIMP 6.5 ISO.