tests/qtest/cdrom-test: Fix the test to also work without optional devices

It's possible to disable virtio-scsi and virtio-blk in the binaries,
so we must not run the corresponding tests if these devices are missing.

Message-Id: <20230512124033.502654-14-thuth@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed