ci: revert ibm canary test to ubuntu 18
ci: revert ibm canary test to ubuntu 18

The ibm test has been failing since the move to ubuntu 20
was merged a couple days ago. Reverting back to 18 for now.

Signed-off-by: Travis Nielsen <a8b474fdb3f77f44446f0ab9ddca8147b09b3a9e@redhat.com>

rook/rook,rook/rook,rook/rook,rook/rook,rook/rook