Configure Pointer Model

An input device is allowed to interact with graphical framebuffer of virtual machines.

According to the type of this input device the movement cursor movement will be different. For instance using a type "Tablet" for absolute cursor movement or "Mouse" for relative.

Currently Nova only supports to configure an input type on bus USB and type "Tablet" but several other possibility should be added. In fact Some operating systems may not support USB or virtual machine running on Xen may prefer using a paravirtualized device.

This blueprint will deprecates option "use_usb_tablet" for a more generic "pointer_model" which will be used to configure default behavior of host. Also a new image propery "hw_pointer_model" will be introduced to give control of user to configure input based on operating system installed in image and use case.

 Possible values:
    - ps2-mouse|xen-mouse|vmware-mouse|usb-mouse|usb-tablet|spice-mouse|virtio-mouse