Patch sets for usb hotplug function

1) libvirt_bench: Add stress tests for usb-device hotplug function.
2) libvirt: add tests for controller involving usb-device hotplug.
3) libvirt: add tests for usb-device hotplug function
    The test target device includes keyboard, mouse, tablet, and disk.
@will-Do 
Thank you for your comment.
yes,  i want to use result.command and i want to keep it.
i think it's useful.
and i found some sample for "raise error.CmdError ..." at ./virttest/virsh.py
 such as,  raise error.CmdError(cmd, sc_output, "Failed to get list of snapshots")

The other comments has been accepted.
Thanks again.