RFE: rhel 8 public beta DIB element

[Alan Pevec]

There is RHEL 8 Beta public repository available at http://downloads.redhat.com/redhat/rhel/rhel-8-beta/ which could be used to build the rhel-minimal image.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/623137

[Ian Wienand (iwienand)]

A very basic minimal element seems to work based on the public beta per the above change.

To progress this, I want to incorporate simple-init and our gate elements so we have a nodepool-compatable image

There's a few changes outstanding for NetworkManager, which I want for Fedora 29 but will work for RHEL8 beta too

https://review.openstack.org/618962 - fixes a test-case issue with argv
https://review.openstack.org/618963 - code shuffle to reduce churn for next
https://review.openstack.org/618964 - add NetworkManager support
https://review.openstack.org/619119 - skip packages from env var. Required to
https://review.openstack.org/619120 - plumbs through the flags for glean

As we integrate the above, I think we can progress this to a more capable image

[OpenStack Infra (hudson-openstack)]

Change abandoned by Ian Wienand (<email address hidden>) on branch: master
Review: https://review.opendev.org/623137
Reason: support for rhel8 is added with I90540675c70bb475d9db2ae24f81c648a31f3f95