tests: Add s390x-ccw-graphics test case

tests: Add s390x-ccw-graphics test case

We have tests for simple guests with graphics for basically
all other architectures, so it makes sense to include s390x
too.

The input file was generated by running

  $ virt-install \
    --name guest --os-variant fedora29 \
    --vcpus 4 --memory 4096 --disk size=5 \
    --graphics vnc \
    --print-xml

followed by minor tweaks, using a version of virt-manager
that includes commit 7b9de27a990f.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Acked-by: Michal Privoznik <mprivozn@redhat.com>