Use Fedora 29 artifacts instead of Fedora 28, since 28 is now
end-of-life.
Also rename `ci/fah28-insttests.sh` -> `ci/fah29-insttests.sh`
and use the https://getfedora.org/atomic_qcow2_latest redirect
URL for the latest Fedora Atomic Host 29 image.
Closes: #1871
Approved by: jlebon
Robert Fairley