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>
The link you give to me I cannot open.
I execute the test on RHEL7GA, and libvirt version is `library: libvirt 1.1.1`. I use it this way to set the disk to be readonly and shareable. Without this way, I cannot set it to be both modes for my poor knowledge(If you have command way to set it, please tell me :))
And yes, in manpage the explanation of --shareable is `an alias for --mode shareable`, so the option's purpose is to make the mode can be set to both readonly and shareable, so I thinks the fixture you mentioned maybe wrong, if not, I think this option has no meaningful.