- fix SLE 15 configurations
- Fix dist autodetection for sle15-sp2

- Fix crash when using preinstall dependency expansion in OBS
- build-vm-kvm: use /boot/kernel.obs.build and /boot/initrd.obs.build
as fallback regardless of the platform to have a global fallback
kernel to use for distros that do not use the "kernel-obs-build"
package to provide the guests kernel and initrd as the system
binaries are not reliable for use in a guest system
- use abuild user if $NOROOTFORBUILD is set.

- fix createrepo existens check for appimager and docker builds
in chroot
- support to use virt-make-fs for ext3 VM builds

- Arch Linux zstd format support
- fix testbuild fail with latest rpm in SP2 and Leap 15.2
- do not retry automatically on disk full error