bvirt_xml-accessor: modify class XMLElementInt.

Add a carry into __slots__ and make XMLElementInt be able to
handle more kinds of integer (binary, octal, decimal and hexadecimal).

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Add unittest for new XMLElementInt.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
virsh: Add nodedev_dumpxml in virsh modeule.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
virt: add nodedev_xml into libvirt_xml module.

nodedev_xml for node device refer to http://libvirt.org/formatnode.html.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Add unittest for nodedev_xml.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>