Fedora 31 was retired and the image is gone from mirrors.
heat-cfntools have been dropped from fedora images, disable
the test till that's resolved.
Fix contradicting lower constraints to make lower-constraints job pass.
Change-Id: Id869f83a46454897c2fe7a532eebfa2863befe5e
(cherry picked from commit 61e53c4eca)
(cherry picked from commit 779b39c975)