qemu: block: Add node-names to JSON backing storage strings

Format out the node-name if it was assigned for JSON-based storage
specification.

src/qemu/qemu_block.c

@@ -1013,5 +1013,10 @@ qemuBlockStorageSourceGetBackendProps(virStorageSourcePtr src)
         break;
     }
 
+    if (virJSONValueObjectAdd(fileprops, "S:node-name", src->nodestorage, NULL) < 0) {
+        virJSONValueFree(fileprops);
+        return NULL;
+    }
+
     return fileprops;
 }