Added support for HVX in lib/nova

Signed-off-by: Tal Kain <tal.kain@ravellosystems.com>
changed libvirt's default hypervisior to be hvx

Signed-off-by: Tal Kain <tal.kain@ravellosystems.com>
Allowed all hosts filter and configured the usage of usb tablet to false

Signed-off-by: Tal Kain <tal.kain@ravellosystems.com>