RockyLinux 8/9 support

[0x00ace]

Added support for RockyLinux 8/9

I have successfully created images using commands:

magnum-cluster-api-image-builder \
  --operating-system rockylinux-8 \
  --version v1.27.11 \
  --image-builder-version v0.1.25

magnum-cluster-api-image-builder \
  --operating-system rockylinux-9 \
  --version v1.27.11 \
  --image-builder-version v0.1.25

And I have successfully booted Kubernetes clusters using these images

/build-new-images

[mnaser]

Thank you for your contribution! This is great, seems like the failure is unrelated. I am working on a few improvements in #327 so we can actually do a few things:

• Test this code to build images
• Run RockyLinux built images through CI
• Test bumping the image-builder version globally so it works out of the box

[mnaser]

I think we're probably good to land this, since you made a PR from your own fork, Jenkins won't take this into place. I'll merge and see how it goes.