tests/qtest: Add s390x boot order tests to cdrom-test.c

tests/qtest: Add s390x boot order tests to cdrom-test.c

Add two new qtests to verify that a valid IPL device can successfully boot after
failed IPL attempts from one or more invalid devices.

cdrom-test/as-fallback-device: Defines the primary boot target as a device that
is invalid for IPL and a second boot target that is valid for IPL. Ensures that
the valid device will be selected after the initial failed IPL.

cdrom-test/as-last-option: Defines the maximum number of boot devices (8)
where only the final entry in the boot order is valid. Ensures that a valid
device will be selected even after multiple failed IPL attempts from both
virtio-blk and virtio-scsi device types.

Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20241020012953.1380075-20-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>