libvirt security, bug fix, and enhancement update

libvirt-0.9.10-21.0.1.el6 - Replace docs/et.png in tarball with blank image libvirt-0.9.10-21.el6 - qemu: Rollback on used USB devices rhbz743671 - qemu: Dont delete USB device on failed qemuPrepareHostdevUSBDevices rhbz743671 - Revert 'rpc: Discard non-blocking calls only when necessary'...