This makes the two rpm-ostree tests written for IoT - overlaying
and rebasing - work across all rpm-ostree-based flavors we
currently test (IoT, CoreOS and Silverblue) and runs them on
all those flavors.
This requires some other changes. For the Workstation ostree
installer update tests, we have install_default_update_ostree
upload a disk image and run these tests on that image. That means
install_default_update_ostree cannot use a scratch disk (as if
we boot it with two disks but only upload one, the subsequent
tests fail to boot, looking for the missing second disk), but its
specified disk size should be large enough for all updates.
Signed-off-by: Adam Williamson <awilliam@redhat.com>
