Description of problem:

The purpose of this RFE is to support normal behavior of USB passthrough within the same way as it supposed to be on a non virtual machine. 

Currently when disconnecting USB device attached to VM, it can't be connected again unless the VM is restarted.
Furthermore, USB device can't be replaced with other USB device, unless the user power off VM -> detach USB port from VM -> refresh host capabilities -> attach USB port back to VM -> start VM again.

Version-Release number of selected component (if applicable):
rhevm-3.6.0.1-0.1.el6 (3.6.0-17)
vdsm-4.17.10-5.el7ev.noarch
qemu-kvm-rhev-2.3.0-31.el7.x86_64
libvirt-client-1.2.17-5.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Attach USB DOK to VM and run VM.
2. Unplug USB device and plug it again / Replace USB DOK with USB keyboard.
3. 

Actual results:
1. USB DOK attached to VM.
2. USB device remain unplugged.

Expected results:
USB device should be connected back to VM, regardless to USB product type.

Additional info: