Introduce new container image for Rocky Linux, a downstream clone of Red
Hat Enterprise Linux.
Keep non-voting in Check for a while before adding to any gate checks
Signed-off-by: Neil Hanlon <neil@shrug.pw>
Change-Id: Ib383f60bc23b434b400f85c376840a000cafc697
Related-Bug: https://review.opendev.org/805800/
