Merge BadRequest tests of "attach interfaces" API

In test_attach_interfaces, there are BadRequest tests of "attach interfaces".
Most parts of them are duplicated.
This patch merges them for the readability and clarifying their purposes.

Change-Id: Ib9dd2840be46dec6b70fe9e3fda35de88f84b4a9
libvirt: fix _disk_resize to make sure converted image will be restored

During the process of resizing disk if an image is in qcow2 with
partition less the process converts the image to raw.
After the extend we should to restore the original format in all cases
not only if 'use_cow_images' is configured to True.

Change-Id: I792e0fb986a6c5cf9ac477cef0949c8a40099faa
Closes-Bug: #1298976
Merge "libvirt: fix _disk_resize to make sure converted image will be restored"
Merge "Merge BadRequest tests of "attach interfaces" API"