Since qemu 3.1x introduction in Tumbleweed it is no more possible to use osc
build with virtual VM

Skipping verification of package signatures due to secure VM build
Writing build configuration
Running build
VM_ROOT: /tmp/obsbuild.img, VM_SWAP: /tmp/obsbuild.swap
0+0 records in
0+0 records out
0 bytes copied, 1.792e-05 s, 0.0 kB/s
0+0 records in
0+0 records out
0 bytes copied, 2.3351e-05 s, 0.0 kB/s
Creating ext4 filesystem on /tmp/obsbuild.img
tune2fs 1.44.4 (18-Aug-2018)
Setting maximal mount count to -1
logging output to
/media/extras/obsbuild/home:bruno_friedmann:branches:security:netfilter/shorewall/openSUSE_Tumbleweed-x86_64/.build.log...
[    0s] Using
BUILD_ROOT=/media/extras/obsbuild/home:bruno_friedmann:branches:security:netfilter/shorewall/openSUSE_Tumbleweed-x86_64/.mount
[    0s] Using BUILD_ARCH=x86_64:i686:i586:i486:i386
[    0s] Doing kvm build in /tmp/obsbuild.img
[    0s] 
[    0s] 
[    0s] qt-kt started "build shorewall.spec" at Thu Jan 17 08:31:33 UTC 2019.
[    0s] 
[    0s] 
[    0s] processing recipe
/ioda/home/bruno/openSUSE/obs/home:bruno_friedmann:branches:security:netfilter/shorewall/shorewall.spec
...
[    0s] running changelog2spec --target rpm --file
/ioda/home/bruno/openSUSE/obs/home:bruno_friedmann:branches:security:netfilter/shorewall/shorewall.spec
[    0s] init_buildsystem --configdir /usr/lib/build/configs --cachedir
/var/cache/build --prepare --clean --rpmlist /tmp/rpmlist.bpnmJf
/ioda/home/bruno/openSUSE/obs/ho.
[    0s] cycle: rpm-config-SUSE -> rpm
[    0s]   breaking dependency rpm-config-SUSE -> rpm

...

[    4s] booting kvm...
[    4s] /usr/bin/qemu-kvm -nodefaults -no-reboot -nographic -vga none -cpu
host -object rng-random,filename=/dev/random,id=rng0 -device
virtio-rng-pci,rng=rng0 -runas q8
[    4s] qemu-system-x86_64: -drive
file=/tmp/obsbuild.img,format=raw,if=none,id=disk,serial=0,cache=unsafe: Block
format 'raw' does not support the option 'serial'
[    4s] No buildstatus set, either the base system is broken
(kernel/initrd/udev/glibc/bash/perl)
[    4s] or the build host has a kernel or hardware problem...

Build should be adapted quickly to be kept in pace with newer qemu