Add RockyLinux support (backport #263)

[mergify]

This is an automatic backport of pull request #263 done by Mergify.
Cherry-pick of 807bc9c has failed:

On branch mergify/bp/quincy/pr-263
Your branch is ahead of 'origin/quincy' by 2 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 807bc9c.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   cephadm-preflight.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   tox.ini

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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