Windows SMBFS: Handle volume_name in _qemu_img_info

The volume_name is now parsed to the _qemu_img_info wrapper. As
this method is not prone to security issues because this driver
does not support raw images (at least not yet), we don't have to
perform any checks on the backing image file path.

Thus, this method simply ignores this argument that will be parsed
by the base class methods.

Related-Bug: #1350504

Change-Id: I801a6338250ec2dc631c4058543f7d0088b3e4d4
Merge "Windows SMBFS: Handle volume_name in _qemu_img_info"