libvirt.test: Add more options test for attach-disk

Add some more test for attach-disk, for example:
--serial, --address, --multifunction, --subdriver, etc.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
@liyangfnst This is what Eric replied. 
```
> I'm inclined to NACK this patch.  Pick one or the other, you can't have
> both
```
So, these two options are orthogonal. We cann't attach disk with both modes.