qemu.tests.usb_basic_check: Add a step for checking dmesg msg

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.test.usb_hotplug: Add a negative test

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.tests.cfg: Add test for 8 devices on usb-hub

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.test.usb_hotplug: Get usb device type from its own params

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
virt.qemu_vm: Add missing equal sign

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
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.