namespace: make sure InaccessibleDirectories= masks all mounts further down

If a dir is marked to be inaccessible then everything below it should be masked
by it.

src/test/test-ns.c

@@ -26,6 +26,7 @@
 int main(int argc, char *argv[]) {
         const char * const writable[] = {
                 "/home",
+                "/home/lennart/projects/foobar", /* this should be masked automatically */
                 NULL
         };
 
@@ -42,11 +43,12 @@ int main(int argc, char *argv[]) {
         };
         char *root_directory;
         char *projects_directory;
-
         int r;
         char tmp_dir[] = "/tmp/systemd-private-XXXXXX",
              var_tmp_dir[] = "/var/tmp/systemd-private-XXXXXX";
 
+        log_set_max_level(LOG_DEBUG);
+
         assert_se(mkdtemp(tmp_dir));
         assert_se(mkdtemp(var_tmp_dir));