Upstream git has a fixed version here:
https://github.com/mattiasgiese/spacewalk/blob/5e7c10b6e61f4bc3249b2764a2c770b7b25e2349/client/rhel/rhn-client-tools/src/up2date_client/hardware_udev.py#L337

Basically python-pyudev is used wrong which leads to a backtrace when
registering a new client.

Reproducable: always
OS: SLES 12 SP2
# rpm -qa | grep -e rhn -e spacewalk -e pyudev -e gudev
rhnsd-5.0.33-2.1.x86_64
libgudev-1_0-0-230-1.5.x86_64
python-pyudev-0.16.1-1.11.noarch
rhnlib-2.8.5-1.1.noarch
python2-rhn-check-2.8.9-1.1.noarch
rhn-setup-2.8.9-1.1.noarch
zypp-plugin-spacewalk-1.0.0-2.1.noarch
python2-rhn-client-tools-2.8.9-1.1.noarch
rhn-check-2.8.9-1.1.noarch
python-gudev-147.2-1.23.x86_64
rhn-client-tools-2.8.9-1.1.noarch
rhn-org-trusted-ssl-cert-1.0-1.noarch
python2-rhn-setup-2.8.9-1.1.noarch