builder: do not use xz --block-size for the test images

Do not use the --block-size parameter of xz when compressing the test
images, as that option does not exist in xz < 5.1.
tests: make the scratch disk used for scratch much larger

50M can be not enough when uploading various copies of unstripped
static binaries from the system, which can fill up such a small disk.
appliance: initial packagelist for OpenSUSE

Mostly complete and making most of the features work.

The notable lack is ntfsprogs and ntfs-3g, which due to the way
mount.ntfs is handled (i.e. using alternatives) do not work properly.