Add unittest file for basic:label

src/basic/label.c

@@ -28,3 +28,7 @@ int label_ops_post(int dir_fd, const char *path) {
 
         return label_ops->post(dir_fd, path);
 }
+
+void label_ops_reset(void) {
+        label_ops = NULL;
+}

src/basic/label.h

@@ -12,3 +12,4 @@ int label_ops_set(const LabelOps *label_ops);
 
 int label_ops_pre(int dir_fd, const char *path, mode_t mode);
 int label_ops_post(int dir_fd, const char *path);
+void label_ops_reset(void);