Fix the wrong params of attach/detach interface for compute driver

The reason of attach_interface failed is current code passing VIF object
to attach_interface, but it expected NetworkInfo object. And as the
comment of attach/detach_interface, they should only accept one
interface to instance. So correct the interface signature only accept
an VIF object. And correct the fake driver behavior, make the test running
correctly.

Change-Id: Id0d28c39fb543853bd710fcb3c3b611306b4fb8f
Close-bug: #1233504
Merge "Fix the wrong params of attach/detach interface for compute driver"