Merge pull request #525 from zhouqt/usb

qemu: Add 3 tests steps for usb testing

* Check dmesg output after booting with usb device.
* Negative testing for usb hotplug
* Assign max number of devices (8) to usb-hub and check if qemu works well.
net: remove redundant evaluation

Valid ifname is provided and used in open_tap(), the
evaluation in the end is redundant, just remove it.

Signed-off-by: Amos Kong <akong@redhat.com>
add definitions of multiqueue

Signed-off-by: Amos Kong <akong@redhat.com>
net: add multiqueue support

Multiqueue feature was supported by kernel/qemu upstream already,
this patch changed Autotest to support command line.

This change compat old qemu/kernel, it will still use 'fd' when
there is only one queue.

More information about multiqueue:
  http://www.linux-kvm.org/page/Multiqueue
  linux/Documentation/networking/tuntap.txt

Signed-off-by: Amos Kong <akong@redhat.com>
net: update hotplug tests

This patch just makes the cases work. I will change cases really
use multi_queue by another split patchset.

Signed-off-by: Amos Kong <akong@redhat.com>