tests/functional: Add a test for s390x pxelinux.cfg network booting

tests/functional: Add a test for s390x pxelinux.cfg network booting

Check the various ways of booting a kernel via pxelinux.cfg file,
e.g. by specifying the config file name via the MAC address or the
UUID of the guest. Also check whether we can successfully load an
alternate kernel via the "loadparm" parameter here and whether the
boot menu shows up with "-boot menu=on".

Reviewed-by: Jared Rossi <jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250709083443.41574-6-thuth@redhat.com>