this should avoid unnecessary disk uploads and hopefully help
further reduce the incidence of weird failures in the chained
tests.
With this change we should only upload disk images for the cases
where we're actually going to run the chained tests: we won't
upload disk images for default_install runs on images we don't
run the chained tests for, or for the UEFI job for images we
*do* run the chained tests for.
We only actually need to run the current chained tests
for Server DVD, Workstation live and KDE live x86_64; there's
no need to run them for Everything boot, so we drop that.