nodedev: Expose sysfs path of device

The name format is constructed by libvirt, it's not that clear to
get what the device's sysfs path should be. This exposes the device's
sysfs path by a new tag <path>.

Since the sysfspath is filled during enumerating the devices by
either udev or HAL. It's an output-only tag.

src/conf/node_device_conf.c

@@ -236,6 +236,7 @@ char *virNodeDeviceDefFormat(const virNodeDeviceDefPtr def)
 
     virBufferAddLit(&buf, "<device>\n");
     virBufferEscapeString(&buf, "  <name>%s</name>\n", def->name);
+    virBufferEscapeString(&buf, "  <path>%s</path>\n", def->sysfs_path);
     if (def->parent) {
         virBufferEscapeString(&buf, "  <parent>%s</parent>\n", def->parent);
     }