Add getter and setter of seclabel into vm_xml module.

(1).Add @staticmethod get_seclabel(vm_name, virsh_instance=virsh)
into vm_xml.
(2).Add @staticmethod set_seclabel into vm_xml.

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

(1).add seclabel into dumpxml of dummy_virsh.
(2).add test_seclabel in VMXMLTest.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Add utils_selinux in virttest.

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

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Add svirt test module in libvirt.

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